Compare Images

I need a portion of code/algorithm to compare two images and give a objective score as to their similarity. The code just needs to accept two 8x8 pixels images (or square position in a larger picture) - and give a rating as to how similar thay are. I want to know how similer they are to the human eye. I want to go beyond just calculating the absolute difference between colours, as it might be that the whole picture is one value darker, but to the human eye looks identical. Whereas a image that has the a different shape in it might end up with the same difference value. I am more interested in objective difference - like shape and colour than exact difference. This is part of a bigger project that needs to find the closest match from a set of pictures. I have been unable to find a suitable solution to matching pictures. As there is no right/wrong solution, i am willing to accept any reasonable suggestion, as long as it goes beyond just calculating the sum difference of each pixel. Samples can be seen on this page: <[login to view URL]> ## Deliverables 1) functional working demo program(s) in as well as complete source code of all work done. 2) All deliverables will be considered "work made for hire" under U.S. Copyright law. Buyer will receive exclusive and complete copyrights to all work purchased. (No GPL, GNU, 3rd party components, etc. unless all copyright ramifications are explained AND AGREED TO by the buyer on the site per the coder's Seller Legal Agreement). ## Platform PHP - to run on a linux webserver. I am open to offers if someone has a solution on a different platform, i will then intergrate it with my solution.