title: C# hashing and looking up images
body: <p>I'm currently at the point where I can convert Bitmap into byte arrays.  Suppose I have 26 images representing a-z with 26 corresponding byte arrays.  Given an image I would like to use the byte array to instantly lookup the correct letter rather than performing up to 26 comparisons.  Is there some way of hashing the byte arrays to produce a hash code that can be stored in a configuration file?</p>
  
  <p>Alternatively if there is a better (faster) approach than hashing the images (assuming I have no access to the underlying textual representation) I would very much like to know about them. For clarification purposes suppose I have "a.bmp", "b.bmp" etc.  I now have an unknown image on the screen.  I would have thought hashing the image and performing a single lookup would be the fastest way for a positive identification.  It should be faster than performing up to 26 individual comparisons.  If this assumption is incorrect, I would appreciate an outline of the optimal method.</p>
  
  <p>Note: It's not a classic OCR problem (handwriting recognition etc) because the letters will be rendered identically every time.  Therefore the letter "a" will always produce exactly the same hash code</p>