Hi, it depends what you like to match. If the pictures need to be exactly == binary identical, you could just use a md5 checksum, or something like this. If you want to search for "similar" pictures e.g. showing the same thing but scaled (image for email, etc. ) then you could use a cooccourence matrix over the colors in the image. If you want to check also if the contrast was changed then you need an even more elaborate algorithm, maybe doing a color histogram and then do a cross correllation. But these are only ideas... Regards, Tobias