modes for implementing the invention ( hereinafter referred to as embodiment ) will now be described in the following order . 1 . embodiment ( example in which light sources are provided in a tilted disposition ) fig4 shows an exemplary configuration of an image processing device 41 according to an embodiment of the invention . the image processing device 41 includes a camera 61 , light source groups 62 , a light source control section 63 , a controller 64 , a camera control section 65 , and an image processing section 66 . the camera 61 images an object ( object to be imaged ) and supplies an image obtained by imaging the object to the camera control section 65 . the light source groups 62 include a light source 81 , another light source 82 , and a support base 83 . for example , the light source 81 is an led , and the light source radiates illumination light having a wavelength λ 1 ( e . g ., near infrared light having a wavelength of 870 nm ). for example , the light source 82 is an eld , and the light source radiates illumination light having a wavelength λ 2 which is different from the wavelength λ 1 ( e . g ., near infrared light having a wavelength of 950 nm ). the support base 83 supports the light sources 81 and 82 such that an object to be imaged is illuminated by illumination light radiated by the light sources 81 and 82 . the image processing device 41 includes a plurality of light source groups 62 . the number of the light source groups 62 disposed and the positions of the light source groups will be described later with reference to fig5 , 6 , and 10 which will be described later . the light source control section 63 controls the light source 81 to cause it to radiate illumination light having the wavelength λ 1 . the light source control section 63 also controls the light source 82 to cause it to radiate illumination light having the wavelength λ 2 . the controller 64 controls the light source control section 63 and the camera control section 65 . in response to the control by the controller 64 , the camera control section 65 controls the imaging by the camera 61 . the camera control section 65 supplies an image imaged by the camera 61 to the image processing section 66 . the image processing section 66 detects , for example , a skin area included in the image supplied from the camera control section 65 . the image processing section 66 performs processes associated with the detected skin area . an example of the disposition of the light source groups 62 will be described with reference to fig5 and 6 . fig5 is a plan view of the image processing device 41 taken from a point on a z - axis , and fig6 is a perspective view of the image processing device 41 . in order to avoid complicatedness of illustration , fig5 and 6 show only the camera 61 and the light sources 81 and 82 ( of the light source groups 62 ), and the light source control section 63 , the controller 64 , the camera control section 65 , the image processing section 66 , and the support base 83 are omitted in the illustration . referring to fig5 and 6 , two light source groups 62 a and 62 b are used as the light source groups 62 . the camera 61 is disposed on the origin of an xyz coordinate system such that a reference axis of the camera 61 coincides with the y - axis . the reference axis is an imaginary line which extends in the normal direction of a lens surface of the camera 61 ( the imaging direction of the camera 61 ) and which extends through the center of the lens surface ( the so - called optical axis of the lens ). the light source group 62 a is constituted by a light source 81 a radiating illumination light having the wavelength λ 1 and a light source 82 a radiating illumination light having the wavelength λ 2 . the light source group 62 b is constituted by a light source 81 b radiating illumination light having the wavelength λ 1 and a light source 82 b radiating illumination light having the wavelength λ 2 . the light source groups 62 a and 62 b are disposed in such positions on the xz plane defined by the x - axis and the z - axis that the light source groups are symmetric about the reference axis of the camera 61 ( y - axis ). the term “ symmetric ” in this context is used to represent a situation in which the light source groups 62 a and 62 b are disposed point - symmetrically about the reference axis of the camera 61 acting as the axis of symmetry ( i . e ., disposed point - symmetrically about the origin of the xyz coordinate system where the reference axis of the camera 61 and the xz plane intersect each other ) or a situation in which the light source groups 62 a and 62 b are disposed line - symmetrically about a straight line which orthogonally intersects the reference axis of the camera 61 ( y - axis ) and which also orthogonally intersects the x - axis , the straight line ( i . e ., the z - axis ) serving as an axis of symmetry . further , the light source 81 a of the light source group 62 a is disposed in such a position that a mechanical axis a of the light source 81 a extends through an object to be imaged . the mechanical axis a is an axis extending through the light source 81 a substantially in the middle thereof and extending in parallel with the direction in which a maximum illuminance distribution is obtained . similarly , the light source 82 a is disposed in such a position that a mechanical axis of the light source 82 a extends through the object to be imaged . the light source 81 b of the light source group 62 b is disposed in such a position that a mechanical axis b of the light source 81 b extends through the object to be imaged . the mechanical axis b is an axis extending through the light source 81 b substantially in the middle thereof and extending in parallel with the direction in which a maximum illuminance distribution is obtained . similarly , the light source 82 b is disposed in such a position that a mechanical axis of the light source 82 b extends through the object to be imaged . referring to fig5 and 6 , a tilt angle θ ( deg ) is an angle at which the mechanical axis a is tilted toward the y - axis ( an angle defined by a line segment 101 in parallel with the y - axis and the mechanical axis a ), an angle at which the mechanical axis of the light source 82 a is tilted toward the y - axis , an angle at which the mechanical axis b is tilted toward the y axis ( an angle defined by a line segment 102 in parallel with the y - axis and the mechanical axis b ), or an angle at which the mechanical axis of the light source 82 b is tilted toward the y - axis . the light source groups 62 a and 62 b are disposed such that the mechanical axes of the light sources 81 a , 81 b , 82 a , and 82 b are tilted toward the y - axis at the same tilt angle θ ( tilted disposition ). the distance l [ m ] in fig5 and 6 is the distance between the light source groups 62 a and 62 b . the tilt angle θ is set within the range from about 3 deg to about 45 deg . the distance l is set according to the set tilt angle θ such that each of the mechanical axes extends through the object to be imaged at that angle . such a configuration is adopted because an experiment carried out by the inventors revealed that tilt angles θ set within the range from about 3 deg to about 45 deg provide relatively good results . the experiment carried out by the inventors will now be briefly described . the inventors carried out an experiment on the image processing device 41 having the light source groups 62 a and 62 b . specifically , an illuminance ratio variation index α and a luminous quantity index β were calculated for each of combinations ( θ , l ) of the tilt angle θ and the distance l at which the light source groups 62 a and 62 b were disposed such that the respective mechanical axes would extend through an object to be imaged . the illuminance ratio variation index α is an index indicating the degree of coincidence between illuminance distributions of light rays having the wavelengths λ 1 and λ 2 . the luminous quantity index β is an index which is proportionate to the luminous quantity of illumination light illuminating an object to be imaged . the illuminance ratio variation index α and the luminous quantity index β will be described later in detail . in this experiment , a camera having a field angle of 29 . 6 deg in the x - axis direction ( horizontal direction ) and a field angle of 22 . 4 deg in the z - axis direction ( vertical direction ) was used as the camera 61 . further , leds emitting ( radiating ) illumination light ) at an emission angle of 16 deg were used as the light sources 81 a and 81 b , and leds having an emission angle of 21 deg were used as the light sources 82 a and 82 b . results of the experiment carried out by the inventors will now be detailed with reference to fig7 and 8 . relationship between tilt angle θ and illuminance ratio variation index α fig7 shows a relationship between the tilt angle θ and the illuminance ratio variation index α . in fig7 , the horizontal axis represents the distance from the camera 61 to the object to be imaged , and the vertical axis represents the illuminance ratio variation index α are shown . an illuminance ratio variation index α is a maximum value max |( i1 − i2 )/ ave | among absolute values of a plurality of quotients |( i1 − i2 )/ ave | where ( i1 − i2 ) represents differences ( i1 − i2 ) between pixel values i1 of pixels forming a first image obtained by imaging the object and pixel values i2 of pixels forming a second image obtained by imaging the object and corresponding to the pixels of the first image and where “ ave ” represents an average of luminance values of the pixels forming the first and second images . great and small absolute values |( i1 − i2 )/ ave | are calculated with greater differences in magnitude at higher scatterdness , the higher the degree of non - coincidence between the illuminance distributions of interest . values calculated as absolute values |( i1 − i2 )/ ave | are smaller , the higher the degree of coincidence between the illuminance distributions . therefore , the maximum value max |( i1 − i2 )/ ave | is smaller ( closer to 0 ), the higher the coincidence between the illuminance distributions . the curve represented in a thin line ( thin solid line ) in fig7 is a plot obtained when the combination ( θ , l ) is ( 0 , 0 ). the curve represented in a dotted line is a plot obtained when the combination ( θ , l ) is ( 9 , 0 . 5 ). the curve represented in a finer dotted line ( dotted line formed by a greater number of dots ) is a plot obtained when the combination ( θ , l ) is ( 18 , 1 ). the curve represented in a chain line is a plot obtained when the combination ( θ , l ) is ( 34 , 2 ). the curve represented in a two - dot chain line is a plot obtained when the combination ( θ , l ) is ( 45 , 3 ). the curve represented in a thick ( thick solid line ) is a plot obtained when the combination ( θ , l ) is ( 53 , 4 ). as shown in fig7 , the illuminance ratio variation index α is closer to 0 , the greater the tilt angle θ . that is , the degree of coincidence between illuminance distributions is higher , the greater the tilt angle θ . the degree of coincidence between illuminance distributions increases with the tilt angle θ for the reason described below . the distance between the light source groups 62 a and 62 b of the image processing device 41 and an object to be imaged increases with the tilt angle θ . illumination light radiated from the light source 81 a in a direction parallel to the mechanical axis a illuminates the object to be imaged with a more uniform optical intensity , the greater the distance between the light source and the object . similarly , illumination light radiated from the light source 82 a in a direction parallel to the mechanical axis thereof illuminates the object to be imaged with a more uniform optical intensity , the greater the distance between the light source and the object . illumination light radiated from the light source 81 b in a direction parallel to the mechanical axis b illuminates the object to be imaged with a more uniform optical intensity , the greater the distance between the light source groups 62 a and 62 b and the object . similarly , illumination light radiated from the light source 82 b in a direction parallel to the mechanical axis thereof illuminates the object to be imaged with a more uniform optical intensity , the greater the distance between the light source groups 62 a and 62 b and the object . that is , illumination light having the wavelength λ 1 radiated from the light sources 81 a and 81 b at certain timing has a more uniform optical intensity , the greater the distance between the light source groups 62 a and 62 b and the object to be imaged . illumination light having the wavelength λ 2 radiated from the light sources 82 a and 82 b at different timing has a more uniform optical intensity , the greater the distance between the light source groups 62 a and 62 b and the object to be imaged . in this case , the illumination light of the wavelength λ 1 having a uniform optical intensity is radiated to obtain a uniform illuminance distribution by the light having the wavelength λ 1 at the first timing . at the different or second timing , the illumination light of the wavelength λ 2 having a uniform optical intensity is radiated to obtain a uniform illuminance distribution by the light having the wavelength λ 2 . therefore , the illuminance distribution of the light having the wavelength λ 1 and the illuminance distribution of the light having the wavelength λ 2 are more uniform , the greater the distance between the light source groups 62 a and 62 b and the object to be imaged ( the greater the tilt angle θ ). thus , non - coincidence between the illuminance distributions of the light rays having the wavelengths λ 1 and λ 2 can be more effectively suppressed ( a higher degree of coincidence can be achieved between the illuminance distribution , the greater the distance . fig8 shows a relationship between the tilt angle θ and the luminous quantity index β . in fig8 , the horizontal axis represents the distance from the camera 61 to an object to be imaged . the vertical axis of the figure represents the luminous quantity index β . the luminous quantity index β is an index which is proportionate to a total luminous quantity obtained by integrating quantities of light radiated to an imaging range of the camera 61 ( a range which includes the object to be imaged ). fig8 shows curves obtained by various combinations ( θ , l ) of the tilt angle θ and the distance l in the same manner as in fig7 . as shown in fig8 , as the tilt angle θ increases , the distance l and the distance between the object to be imaged and each of the light source groups 62 a and the light source group 62 b increase . therefore , the luminous quantity index β decreases as the tilt angle θ increases . that is , the luminous quantity of illumination light illuminating the object to be imaged ( imaging range ) decreases , as the tilt angle θ increases . referring to fig7 , when the distance from the camera 61 to the object to be imaged ( represented by the horizontal axis of the figure ) is about 1 . 5 m , the illuminance ratio variation index α has a relatively small value regardless of the combination ( θ , l ) used . referring to fig8 , when the distance from the camera 61 to the object to be imaged is in the range from about 1 . 5 m to about 1 . 8 m , the luminous quantity index β has a relatively great value regardless of the combination ( θ , l ) used . an experiment was conducted with the distance from the camera 61 to an object to be imaged set at 1 . 5 m to find a tilt angle θ at which illuminance distributions of illumination light rays having the wavelengths λ 1 and λ 2 illuminating the object have a high degree of coincidence and at which the illumination light rays have a great luminous quantity to allow a skin area to be accurately detected from a first image obtained by imaging the object . as a result of the experiment conducted with the distance from the camera 61 and the object to be imaged set at 1 . 5 m , most of a skin area such as a hand or arm could be accurately detected with the when the tilt angle θ was set at 3 deg because the luminous quantity index β had a sufficiently great value at that angle although the illuminance ratio variation index α was somewhat great . as a result of the experiment conducted with the distance from the camera 61 and the object to be imaged set at 1 . 5 m , the illuminance ratio variation index α had a small value and non - coincidence between illuminance distribution was sufficiently low when the tilt angle θ was set at 46 deg or more . however , the luminous quantity index β also had a small value , and the luminous quantity of the illumination light illuminating the object to be imaged was therefore insufficient . therefore , the object such as a hand or arm could not be accurately detected in some occasions . therefore , the tilt angle θ is set within the range from about 3 deg to about 45 deg in the present embodiment . the distance l is uniquely set ( determined ) according to the setting of the tilt angle θ . thus , the image processing device 41 can accurately detect a skin area such as a hand or arm . let us now discuss an optimal value of the tilt angle θ at which a skin area such as a hand or arm can be most accurately detected among the angles in the range from 3 deg to 45 deg that can be set as the tilt angle θ . for example , when the tilt angle 0 is 45 deg , the intensity of illumination light illuminating an object to be imaged decreases about 5 % each time the distance from the camera 61 to the object to be imaged changes by 10 cm . the description has been made on an assumption that an object to be imaged exists in a position 1 . 5 m apart from the camera 61 . in practice , however , an object to be imaged is not necessarily located just 1 . 5 m apart from the camera 61 . therefore , in order to detect a skin area of an object to be imaged from a first image obtained by imaging the object even when the object is located , for example , about 10 cm beyond the distance of 1 . 5 m , it is necessary to maintain the intensity of illumination light ( the luminous quantity of illumination light ) such that an about 5 to 10 percent difference between reflectances of light rays having the wavelengths λ 1 and λ 2 can be detected . as described above , when the tilt angle θ is 45 deg , the intensity of illumination light illuminating an object to be imaged decreases by about 5 % each time the distance from the camera 61 to the object to be imaged changes by about 10 cm . in the case of an object to be imaged located about 10 cm beyond such the distance of 1 . 5 m , it may be difficult in some occasions to maintain the intensity of the illumination light such that an about 5 to 10 percent difference between reflectances of light rays having the wavelengths λ 1 and λ 2 can be detected . for example , when the tilt angle is 34 deg , each time the distance from the camera 61 to an object to be imaged changes by about 10 cm , the intensity of illumination light illuminating the object to be imaged undergoes a decrease that is only about one half of the decrease that occurs when the tilt angle θ is 45 deg . therefore , when the tilt angle θ is 34 deg , even in illuminating an object to be imaged located about 10 cm beyond the distance of 1 . 5 m , the intensity of the illumination light can be kept at such a level that an about 5 to 10 percent difference between reflectances of light rays having the wavelengths λ 1 and λ 2 can be detected . thus , when the distance from the camera 61 to an object to be imaged is 1 . 5 m , the optimal tilt angle is 34 deg . as described above , the light source groups 62 ( e . g ., the light source groups 62 a and 62 b ) of the present embodiment are disposed such that the mechanical axes of the light sources 81 ( e . g ., the light sources 81 a and 81 b and the light sources 82 ( e . g ., the light sources 82 a and 82 b ) are tilted toward the reference axis at the same tilt angle θ . it is therefore possible to suppress non - coincidence between illuminance distributions of light rays having the wavelengths λ 1 and λ 2 . therefore , even when the light sources 81 an the light sources 82 are different from each other in directivity , non - coincidence between illuminance distributions of light rays having the wavelengths λ 1 and λ 2 can be suppressed by tilting the light source groups 62 . as a result , the light source groups 62 of the image processing device 41 can be formed in various configurations by combining the light sources 81 and light source 82 appropriately without a need for paying attention to the difference between the light sources 81 and 82 in terms of directivity . in the present embodiment , since the light source groups 62 are provided in a tilted disposition , an object to be imaged can be illuminated such that less parts of the object will be left unilluminated or shaded , when compared to illumination carried out using light sources disposed , for example , as shown in fig3 . thus , the image processing device 41 can acquire first and second images for detecting a skin area more accurately . since the tilted disposition of the light source groups 62 makes it possible to illuminate a greater area of an object to be illuminated , the number of each of the light sources 81 and 82 can be kept as small as two at the minimum ( for example , the light sources 81 may be constituted by two light sources , i . e ., the light sources 81 a and 81 b ). thus , the image processing device 41 can be manufactured as a low manufacturing cost . in the present embodiment , the two light source groups 62 a and 62 b are provided in a tilted disposition as the light source groups 62 . the number and disposition of the light sources 62 is not limited to the above description . for example , the image processing device 41 may be provided with four light source groups 62 . an example of the disposition of four light source groups 62 will now be described with reference to fig9 and 10 . elements which are similar in configuration between fig9 and 5 and between fig1 and 6 are indicated by like reference numerals , and such elements will not be described below . fig9 and 10 show a configuration which is similar to that shown in fig5 and 6 except that additional light source groups 62 c and 62 d are provided . as shown in fig9 and 10 , the light source groups 62 c and 62 d disposed in positions which are on the z - axis and in which the light sources are symmetric about the reference axis of the camera 61 . the light source groups 62 c and 62 d are provided in a tilted disposition in the same manner as the light source groups 62 a and 62 b . when the number of the light source groups 62 is increased as thus described , the number of shadows generated on an object to be imaged can be reduced . in the above - described embodiment , an object to be imaged is illuminated by illumination light from the light source groups 62 a and 62 b . alternatively , auxiliary light sources radiating light rays having the wavelengths λ 1 and λ 2 , respectively , may be disposed in positions different from the positions of the light source groups 62 a and 62 b . thus , the generation of shadows on an object to be imaged can be suppressed . for example , the auxiliary light sources may be disposed near the reference axis . however , the degree of coincidence between illuminance distributions is more susceptible to variations of the directivity of the auxiliary light sources , the closer the auxiliary light sources to the reference axis . it is therefore desirable to dispose the auxiliary light sources in positions apart from the reference axis . in the above - described embodiment , the light sources 81 radiate light having the wavelength λ 1 of 870 nm , and the light sources 82 radiate light having the wavelength λ 2 of 950 nm . however , the invention is not limited to such a combination of wavelengths . any combination of wavelengths may be employed as long as an absolute difference between reflectance of light having the wavelength λ 1 and reflectance of light having the wavelength λ 2 obtained at the skin of a user is sufficiently greater than an absolute difference between reflectance at other objects . specifically , the light sources 81 and 82 may be configured to radiate illumination light having a wavelength λ 1 of 930 nm or less and a wavelength λ 2 of 930 mm or more , respectively , to use a combination of wavelengths such as a combination of 800 nm and 950 nm , a combination of 870 nm and 1000 nm , or a combination of 800 nm and 1000 nm , instead of the combination of 870 nm and 950 nm . the embodiment of the invention may be used in an electronic apparatus as a computer which performs processes based on results of the detection of a skin area of an image obtained by imaging an object that is illuminated by illumination light rays having different wavelengths . the present application contains subject matter related to that disclosed in japanese priority patent application jp 2009 - 187047 filed in the japan patent office on aug . 12 , 2009 , the entire contents of which is hereby incorporated by reference . it should be understood by those skilled in the art that various modifications , combinations , sub - combinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof .