You have chosen a very difficult project for yourself. Your project (automatically recognizing similar images) is the type of problem that comp-sci graduate students write doctoral thesis about. It is unbelievably difficult to have computers recognize images.

Your program would probably look for distinctive features of the images. Probably simple shapes. The line of the horizon in a shot of the desert. The circle of a noon sun. The rectangle of a television screen. Then, you would compare these shapes to a precompiled database of your other images.

Unfortunately, there are still problems with this approach. Users might have scanned at a different magnification or resolution. Their scan might be cropped differently. Of course, the most daunting challenge is how to program a computer to recognize shapes in an image. I, personally, can't even begin to think of how to do this.

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IndyZ