Hi!
Well, it does have mathematic functions for writing images, but not ones to analyze / read images. These are really low-level C functions that can be found on the net, and they can alalyze the image and return probability of image coincidence. I think I heard about such libraries for Linux desktop toolkit GNOME. Look there. If you know C well enough, you could then make a PHP module, plug it in via dl() call and start analyzing your graphics.
For now you could just use three functions:
- get the physical type of image (extension)
- get the real type, size of image and embedded IPTC markers of the image (use getimagesize (string filename [, array imageinfo]) and compare every returned value. They should be the same.)
- get the file size
or use just one:
- open the files in binary and compare the contents
These should indicate whether files are identical with pretty good probability. Of course they will not help if you have an entire directory of same-size icons, no IPTC markers, same filesize, etc. But I guess you will be comparing JPG or PNG photographs, and the above techniques should be pretty good.
Hope this helps,
Stas
