Perceptual hash implementation for PHP

This is my PHP Implementation of the AverageHash algorithm to create Perceptual Hashes

A perceptual hash is different from a typical hash as it allows you to compute a signature based on the visual features of an image rather than the actual data they contain as with a cryptographic hash. This allows you to use the Perceptual Hash for simple image matching which could prove useful in finding duplicate pictures or picture tagging.

To get a better understanding of this project see: http://www.hackerfactor.com/blog/index.php?/archives/432-Looks-Like-It.html

You can use pHash methods as a class in your project and extend as you wish.

A basic implementation is as follows:

#sample implementation
$phasher = new Phash;
$phash2 = $phasher->getHash('phash2.jpg', false);
//this will echo hash in hex, then binary
echo $phasher->hashAsString($phash2, false).PHP_EOL;
echo $phasher->hashAsString($phash2).PHP_EOL;

$phash3 = $phasher->getHash('phash3.jpg', false);
//this will echo hash in hex, then binary
echo $phasher->hashAsString($phash3, false).PHP_EOL;
echo $phasher->hashAsString($phash3).PHP_EOL;

//using BIT COUNT METHOD FOR SIMILARITY
echo $phasher->getSimilarity($phash2, $phash3, 'BITS');
echo PHP_EOL;

//using HAMMING METHOD (DEFAULT) FOR SIMILARITY
echo $phasher->getSimilarity($phash2, $phash3);
echo PHP_EOL;

• The bitcount algorithm for matching similarity may be siginificantly faster than hamming distance.
• Calculating hamming distance between two hex based hashes may be faster but less accurate than the binary version