in accordance with a first embodiment of the present invention , a document 12 includes plural - bit data steganographically encoded thereon ( e . g ., via digital watermarking ). the document 12 can be a photo id ( e . g ., a driver &# 39 ; s license , student id , identification document , employee badge , passport , etc . ), a value document ( e . g ., a banknote , stock certificate , or other financial instrument ), a credit card , a product manual , bank or credit account card , registration card , an image , a printed document , badge , a photograph , a graphic , or virtually any other type of document or physical object . the encoding of the document 12 can encompass artwork or printing on the document , the document &# 39 ; s background , background pattern or tint , a laminate layer applied to the document , surface texture , pixel or luminance variation , graphic , etc . if a photograph is present , it too can be encoded . a variety of watermark encoding techniques are detailed in the above cited patents and applications ; artisans in the field know many more . the encoded document 12 is presented to an input device 14 for image capture . the input device 14 can include a digital camera , digital camera , web camera , flatbed scanner , a hand scanner ( including an imaging mouse ), a video camera , ccd array , etc ., etc . input device 14 communicates with computer 16 . computer 16 can be a general purpose or dedicated computer , including electronic processing circuitry ( e . g ., a cpu ) 18 , memory 20 , a communication interface 22 ( e . g ., communications port and / or a device driver stored in memory 20 , etc .) with the input device 14 , a monitor or other output device ( e . g ., printer , etc .) 24 , and optionally a network connection ( e . g ., communications hardware and / or software ) 26 . the network connection 26 can be used to connect , e . g ., through an intranet , ethernet , wireless network , internet , or otherwise , to a remote computer ( not shown in fig1 ). the electronic processing circuitry 18 and memory 20 are shown in fig2 . a system communications bus ( not shown ) helps facilitate communication between the various components . suitable software programming instructions , stored in memory 20 for execution by the electronic processing circuitry 18 , can be used to effect various types of functionality for the present embodiment . one such functionality detects and decodes digital watermarks . another functionality provides security for network or computer access . yet another functionality provides document verification for authorized access to a secure area or network location . it should be appreciated that while the fig1 computer system 16 is illustrated as a desktop system , the present invention is not so limited . indeed , the computer system 16 can include a handheld device , a security system , a mobile computer ( e . g ., cell phone , onboard computer , etc .) or a distributed system . similarly , the input device 14 need not be tethered to computer 16 . instead , input device 14 can be integrated with computer 16 and / or can wirelessly or remotely communicate with computer 16 . we initially note that the mere process of giving somebody a security token — be it an identification document , usb token , proximity card , their fingerprint , etc — weakens the security of the system . we believe that using digital watermarks is inherently a more secure method for secure access because digital watermarks can be covert and they can hide in any document . now consider our security enhancements using the fig1 system as an example environment . a document ( e . g ., document 12 ) is steganographically encoded to include a payload having access information . the term “ access information ” is broadly used in this patent document and generally refers to information , which can be used to access , or to determine whether access should be granted , a secure location . a secure location may refer to a physical area , a network resource , a computer file or folder , a software application or computing device , etc . access information may provide a key , code and / or data to allow or determine whether to allow such access . access information may be carried by a steganographic payload ( e . g ., a digital watermark payload ) or can be stored in a data record and accessed with an identifier , e . g ., carried by a steganographic payload . sometimes access information may include a decryption key , and access is allowed when the decryption key is used to successfully decrypt predetermined information . or access information may including information which can be compared to information or samples provided by a user or information retrieved using the access information . in one implementation , a steganographically encoded document 12 is preferably covert , in that a causal visual examination of the document 12 generally does not reveal the steganographic data . as such , document 12 can be placed in a stack of documents ( or if an image , hung on the wall or placed in a frame on a desk ). thus , a would - be - intruder is clueless as to which document , if any , includes the access information . now consider , for example , a new employee &# 39 ; s first day at a secure facility . as she begins her day she is provided with a digitally watermarked document ( e . g ., an id badge or pass ) to allow access into the secure facility or to her computer . the watermark includes a payload having access information . in one implementation , the access information is associated with the employee &# 39 ; s employee number or with the employee &# 39 ; s personal information . ( for example , the access information may include a hash of the employee &# 39 ; s name , birth date , employment start date , favorite xbox ® title or movie , etc . or the access information may include a hash of the employee &# 39 ; s biometric information . the biometric information can be a facial scan / print , fingerprint , retinal identifier , voice sample , dna representation , etc ., etc . for more information on hashing techniques , see e . g ., assignee &# 39 ; s u . s . patent application ser . no . 10 / 027 , 783 , filed dec . 19 , 2001 ( published as us 2002 - 0126872 a1 ), and u . s . patent application ser . no . 10 / 094 , 593 , filed mar . 6 , 2002 ( published as us 2002 - 0170966 a1 ). each of these published u . s . patent documents is herein incorporated by reference .). in another implementation , the access information is selected to match a particular security algorithm for a computer workstation or door access . the employee presents the encoded document 12 to input device 14 . input device 14 captures an image of document 12 and communicates such to computer 16 . steganographic decoding software stored in memory 20 and executed by cpu 18 searches the captured image of document 12 for steganographic encoding , such as a digital watermark . once found , the digital watermark is decoded to recover the digital watermark payload , e . g ., including access information . the access information is then provided to a security software module . ( of course the digital watermark detection software and the security software can be integrated , or can be separate software modules . in some implementations the modules are implemented via hardware .). the security software module uses the payload &# 39 ; access information to determine whether to allow access . for example , the access information may include a code ( e . g ., a numeric or alpha - numeric code ). if the code matches or otherwise coincides with a predetermined code , access is granted . in one implementation , the code is a cryptographic permutation of the predetermined code . the predetermined code can be stored locally in computer 16 or can be retrieved from a central database . the predetermined code can be user specific , for example , the code can be unique per employee . ( a random generator can be used to generate a random code , which is embedded as the payload . the random code is stored in an employee security database record to be indexed with the employee number . in this case , the digital watermark includes the employee &# 39 ; s employee number or other identifier . alternatively , the employee is prompted to enter her employee number , which is used to index the database .). in still another implementation , the employee must provide other access information ( e . g ., birth date , favorite movie title , etc . ), which is then compared to the access information stored on the document . if the access information includes a biometric hash , the user is prompted to provide a biometric sample . for example , if the hash includes retinal scan data , computer 16 preferably includes or communicates with a retinal scanner . the same ( or complimentary ) hashing algorithm is preformed on the retinal scan sample to produce a hash ( i . e ., a “ sampled hash ”). the payload is decoded from the embedded document 12 to retrieve the payload hash . the payload hash is compare with the sampled hash to verify authenticity . if authentic , access is allowed . an employee document 12 can be frequently changed or replaced , e . g ., every day ( or every week , every time the employee leaves a secure facility , etc .). consider an inventive security method with reference to fig3 . at the end of each day , an employee surrenders her watermarked document 12 ( step 30 ) ( in one implementation , surrendering the document 12 unlocks or otherwise opens an exit or door , allowing the employee to leave the premises . in this implementation , the digitally watermarked document 12 must be successfully decoded and verified prior to enabling the exit door .). in a central system , where a watermark detector communicates with a central ( or local ) database , the watermarked document will typically include an employee identifier ( e . g ., employee number ) and steganographically embedded access information . the embedded access information is compared to the database information to determine whether to allow access . the identifier is decoded from the watermark ( step 32 ). the identifier is used to interrogate the database to retrieve the employee &# 39 ; s security watermark access information ( step 34 ). as an optional step , the retrieved access information can be compared with the decode access information to further verify the collected document 12 . new watermark access information ( e . g ., a new code ) is generated ( step 36 ). in some cases the new access information mirrors the old access information . more preferably , however , is to provide entirely new access information . this new access information is used to update the employee &# 39 ; s security watermark access information in the database . a new document 12 ′ is provided to the employee ( step 38 ). the new document 12 ′ includes a steganographic payload with the new access information . to further obscure the security process new document 12 ′ is preferably a new ( or different type of ) document , or differently sized document , perhaps even on a different substrate , etc . ( for example , if document 12 is a traditional employee badge , new document 12 ′ can be a family photograph , graphic or digitally watermarked word or excel document . the new document 12 ′ is used the next day ( or next facility entry ) for building entry , workstation access , etc . the old watermarked document 12 ′ is preferably destroyed and the corresponding old digital watermarked payload ( and code ) is deleted from or marked as inactive in the database . one strength of our inventive system is the fact that outsiders do not know that document 12 or 12 ′ is an access token . this strength becomes evident , for example , when the digital watermark is embedded in a family picture , graphic or arbitrary word / excel document . further , since documents are everywhere — it is extremely difficult for a would - be - thief to know which document is the access token even if they know such documents are used as tokens . not knowing what document is even used , or even that documents are used as the security token enables the security method to remain secret . in another biometric - based implementation , a steganographic payload ( e . g ., a digital watermark payload ) designates a specific “ type ” of biometric data for sampling . one type of biometric data is a fingerprint , another type is behavioral characteristics — including signatures , handwriting and voice patterns , still another type is a retinal scan , other types include face maps , dna samples , blood type , hand geometry , handwriting , iris , vein patterns , and so on . in one example of this implementation , a biometric type is randomly chosen ( or otherwise chosen ). a corresponding biometric sample is taken from a human subject ( e . g ., employee ). the biometric sample is hashed ( or a reduced bit representation of the sample is produced ), and the hash is steganographically encoded in a document . the document also includes biometric “ type ” data to indicate which type of biometric data that the hash represents . to verify authenticity , the encoded document is decoded to retrieve the hash and a biometric “ type ” data . the employee yields a fresh biometric sample of the type indicated by the steganographic type data . a corresponding hashing algorithm is preformed on the fresh biometric sample , and is then compared with the decoded biometric hash . in a second example of this implementation , and with reference to fig4 , an employee provides a plurality of biometric samples , such as at the start of her employment . the biometric samples ( or reduced bit representations of the samples ) are stored in a database 40 , e . g ., according to employee . the employee receives a steganographically encoded document . the steganographic encoding includes a payload 42 — preferably including at least two data fields 42 a and 42 b ( or two types of data ). one field 42 a includes an identifier that is associated with the employee ( e . g ., employee number , etc .). the identifier can be used as an index to interrogate the database 40 , e . g ., to locate a record associated with that particular employee ( e . g ., one of employees a - z ). the second field preferably includes a type of biometric data to sample or test . once a particular employee is identified , the second field can be used to narrow the list of the many stored biometric samples ( e . g ., one of the biometric samples a - z ). ( instead of separate fields , the identifier and biometric type fields can be concatenated as one data string ). the employee presents her steganographically encoded document , which is decoded to retrieve the identifier and biometric type . the biometric type is used to determine which type of biometric information should be sampled . and the identifier ( usually in conjunction with the biometric type ) is used to index database 40 to access an appropriately corresponding stored biometric sample . the stored and fresh biometric samples are compared to determine identity or to determine whether to allow access . of course , the “ type ” field can change each time a document is reissued , such as in the document 12 and document 12 ′ implementation disclosed above . thus , an employee preferably does not know which type of biometric information will be sampled on any given day . in parent application ser . no . 10 / 275 , 197 and pct / us01 / 14014 we disclose a digital watermark - based combination lock . the combination lock responds to a digitally watermarked card positioned at various angles or orientations . a document orientation is analogous to a lock “ tumble .” the card is positioned in a correct sequence of tumbles to unlock the watermark - based combination lock . an alternative to the above - described inventive combination lock requires a user to present a plurality of cards in a proper sequence ( or combination ) to unlock a computer system or secure area . for example , in fig5 a - 5 d , a user must present four digitally watermarked documents in a proper sequence ( e . g ., first present document number 2 , then 3 , then 1 and then 4 ). the documents are distinguished through a digital watermark embedded therein . in one implementation , each watermark includes a unique payload . the access system decodes each payload as the documents are presented in sequence . the system checks with a data record to ensure that the payloads ( or documents ) are presented in a correct or predetermined order . or the payloads can include information to signal which document the system should expect next . still further , a first digital watermark ( e . g ., card 2 ) includes a key to decode ( or decrypt ) a next digital watermark ( e . g ., card 3 ), and so on ; the lock opens if each watermark is successfully decoded . or the unique payload from all cards , when combined , together comprises access information to open the lock . the appropriate combination ( e . g ., sequence of cards ) can be unique per employee or system lock . for example , a digital watermark payload may include the employee &# 39 ; s number . this number is used to interrogate a data record to retrieve a corresponding valid combination . or the employee keys in ( or otherwise enters ) her employee number to retrieve the appropriate data record . in one implementation , a combination comprises a predetermined sequence of cards positioned at differing angles and / or scales . for example , a combination may include a first card having a first identifier and being positioned at a first angle or orientation , and a second card having a second identifier and being positioned at a second angle or orientation . a card &# 39 ; s orientation is readily discernable by a digital watermark orientation component , e . g ., as disclosed in parent application ser . no . 10 / 275 , 197 and pct / us01 / 14014 . in some cases the first card corresponds to a first side of an identification document , and the second card corresponds to a second side of the same identification document . in another implementation , a user must perform the combination in a given amount of time . this restriction helps to prevent a would - be - thief from arbitrarily or systematically presenting different combinations , in hopes of stumbling onto the right combination . alternatively , a predetermined number of consecutive wrongly entered combinations freezes the account or lock . ( for example , after two wrong combination attempts , the lock is frozen and must be reset by a system administrator or via a predetermined procedure , such as with a password / pin .). in still another implementation , each combination lock card includes both a robust and fragile digital watermark . then if someone tries to crack the system by scanning and printing the watermarked cards , the fragile mark predictably degrades or is otherwise lost . the watermark detection software ( and / or access software ) allows access when the cards are shown in the proper order of presentation and they each include both the robust and fragile mark . ( in a related implementation , only one or a few of the combination cards include a fragile watermark . or at least one of the combination cards includes a fragile watermark that converts to a robust watermark upon scanning and printing .). various fragile watermarking techniques can be found , e . g ., in assignee &# 39 ; s u . s . patent application ser . nos . 09 / 234 , 780 , 09 / 433 , 104 , 09 / 498 , 223 , 09 / 562 , 516 , 09 / 567 , 405 , 09 / 625 , 577 , 09 / 630 , 243 , 09 / 645 , 779 , 09 / 689 , 226 , 09 / 689 , 289 , 09 / 689 , 293 , and 09 / 898 , 901 , and in pct patent application no . pct / us02 / 20832 ( published as wo 03 / 005291 ). each of these patent documents is herein incorporated by reference . a specific example of our inventive techniques is now described in relation to a system and method for using a digital watermark embedded in a document to unlock a computer workstation screensaver or sleep mode . with reference to fig1 , in this implementation computer 16 includes logon and screensaver computer software instructions stored in memory 20 for execution on cpu 18 . ( for example , computer 16 includes microsoft windows 2000 , xp , nt , etc ., which has these features .). in some windows versions , a user must toggle ctrl - alt - del before she can log on . this is a security feature to prevent password capturing , e . g ., by a trojan horse program that mimics the logon screen . by hitting the so - called secure attention sequence ctrl - alt - del , control and subsequent keyboard input is passed to the system &# 39 ; s winlogon process . a user logon box is typically presented at this point to prompt the user to enter her username and password . windows can be also configured to activate a screen saver after a predetermined period of non - use ( e . g ., 1 - 5 minutes , etc . ), which is unlocked via a password . our improvement becomes evident at initial logon and / or once a screensaver is activated . take the screensaver case . to access the conventional username / password box , a user first must present a digitally watermarked document for analysis instead of typing ctrl - alt - del . in one implementation , the user shows the digitally watermarked document to an image sensor to activate the username / password box . the image sensor communicates captured image data to a watermark detector . if appropriate access information is encoded with the watermark , the username / password box appears . ( in other implementations , a username / password box is skipped in lieu of the access information .). in another implementation , a keystroke ( or mouse movement ) activates a graphical user interface ( gui ). the gui preferably prompts the user to present her digitally watermarked document . if the watermark is successfully decoded the user is permitted to type in her password . the username / password box is activated only after the user presents the anticipated digitally watermarked document ( e . g ., including a payload with appropriate access information ). of course , the system can be configured to respond variously if a user presents a digitally watermarked document including a payload that does not match or active the screen saver . for example , the system can freeze — requiring a system administrator to unlock the system . or the user can be prompted to present an anticipated digitally watermarked document . from a system level , we can augment the windows login with our digital watermark detection requirements . for example , we can modify or replace the windows gina file ( e . g ., “ msgina . dll ”) to improve the logon process . ( it will be appreciated that gina stands for graphical identification and authorization and describes an interface for the validation of logon credentials .). our modified gina then initiates ( or cooperates with ) watermark detection to facilitate access information authentication . input device 14 captures an image of a digitally watermarked document . a watermark detector analyses the captured image data to detect a digital watermark . a watermark payload or message is decoded once the digital watermark is detected . the payload preferably includes a code or access information to unlock the logon or screensaver . the screensaver is deactivated if the code matches or otherwise provides the predetermined key . otherwise , the user is denied access to the system via the locked screen saver . the user is preferably unable to exit the screensaver or logon process by any method ( e . g ., ctrl - alt - del ) other than using the anticipated watermark and / or the correct password . after successfully entering in the proper password for that access information and / or that workstation , the screensaver will deactivate and return the user to the desktop . in another implementation , the digitally watermarked document provides a necessary password / pin without further user input . in yet another implementation , the digital watermark payload carries an encryption key , which is used to decrypt the computer 16 &# 39 ; s memory or computer files stored in memory . now consider some extensions of our inventive techniques . a document includes a digital watermark having a payload . the payload corresponds to user age group or access permission . the digitally watermarked card is presented to a screen saver , not only to unlock the screen saver , but also to set appropriate computer settings . for example , consider an implementation where the fig1 system resides in a public library . the library wishes to restrict young computer users from accessing pornographic or other mature material . a young user checks in at the library front desk to obtain a digitally watermarked computer access card — which reflect the age group of the young user . the user shows the card to input device 14 to deactivate the screen saver . the digital watermark carries an age indicator that is used by computer system 16 to select an appropriate computer filter ( e . g ., a netnanny ® age - based restriction ) or to restrict certain materials . the foregoing are just exemplary implementations of security systems . it will be recognized that there are a great number of variations on these basic themes . the foregoing illustrates but a few applications of the detailed technology . there are many others . entry of a user &# 39 ; s pin code , or other identity check , may be desirable in certain contexts , e . g ., to guard against granting access to a person who has found or stolen someone else &# 39 ; s card . security is further enhanced when a user possesses both i ) a physical document , and ii ) corresponding verification data ( e . g ., password , pin , retinal scan , voice recognition , biometric verification data , etc ). to illustrate , in order to gain system or network access ( or to login ), a user must demonstrate physical possession of document . a compliant reader reads and extracts embedded data from the document . the embedded data is used to index or otherwise identify corresponding verification data . the corresponding verification data is preferably predetermined and stored for comparison . the user is prompted to provide the verification data ( e . g ., to provide a pin , yield to a fingerprint or retinal scan , etc .). ( the user may be prompted to provide such verification data prior to , or after , presentment of the document ). system access is granted only when the provided verification data correctly corresponds with the predetermined verification data . this multi - step security ( e . g ., physical possession and verification data ) is valuable in many environments , including authentication to a network , access to a software application , verification of identity , verification of permissions , login security , restricted access management , etc . to provide a comprehensive disclosure without unduly lengthening this specification , the above - mentioned patent documents are incorporated herein by reference . having described and illustrated the principles of the invention with reference to illustrative embodiments , it should be recognized that the invention is not so limited . the particular combinations of elements and features in the above - detailed embodiments are exemplary only ; the interchanging and substitution of these teachings with other teachings in this and the incorporated - by - reference patent / applications are also contemplated . for example , the number of documents comprising a combination lock ( e . g ., 4 ) can be varied without departing from the scope of the present invention . in view of the wide variety of embodiments to which the principles and features discussed above can be applied , it should be apparent that the detailed embodiments are illustrative only and should not be taken as limiting the scope of the invention . rather , we claim as our invention all such modifications as may come within the scope and spirit of the following claims and equivalents thereof .