I just found a pretty sweet PHP extension that allows you to easily determine whether 2 pictures are alike. I thought about how I could do this a few years ago, but never really did a whole lot of research on it. I pretty much decided that PHP couldn't deal with the amount of processing power it would take to determine the similarity between two image files. Fortunately, Libpuzzle does exactly that and takes the form of a PHP extension written in C!

The Puzzle library is designed to quickly find visually similar images (gif, png, jpg), even if they have been resized, recompressed, recolored or slightly modified. The library is free, lightweight yet very fast, configurable, easy to use and it has been designed with security in mind.

It's incredibly simple to implement and it seems that most modern website hosts meet the requirements.

Check it out!

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