class Hamming
{
	private function _resizeImage($from_file, $to_file, $width, $height, $quality)
	{
		$img1 = imagecreatefromjpeg($from_file);
		$img2 = imagecreatetruecolor($width, $height);
 
		imagecopyresampled($img2, $img1, 0, 0, 0, 0, $width, $height, imagesx($img1), imagesy($img1));
 
		imagejpeg($img2, $to_file, $quality);
 
		imagedestroy($img1);
		imagedestroy($img2);
	}
 
	private function _grayScaleImage($filename)
	{
		$img_size 	= getimagesize($filename);
		$width 		= $img_size[0];
		$height		= $img_size[1];
		$img 		= imagecreate($width,$height);
 
		for ($c = 0; $c < 256; $c++)
		{
			imagecolorallocate($img, $c, $c, $c);
		}
 
		$img2 = imagecreatefromjpeg($filename);
		imagecopymerge($img,$img2,0,0,0,0, $width, $height, 100);
		imagejpeg($img, $filename);
		imagedestroy($img);
	}
 
	private function _getPixelValue($filename, $x, $y)
	{
		$image 	= imagecreatefromjpeg($filename);
		$color 	= imagecolorat($image, $x, $y);
		$r 		= ($color >> 16) & 0xFF;
		$g 		= ($color >> 8) & 0xFF;
		$b 		= $color & 0xFF;
 
		imagedestroy($image);
 
		return array('r'=>$r, 'g'=>$g, 'b'=>$b);
	}
 
	private function _getChainOfBits($image)
	{
		$tmpfile = sys_get_temp_dir() . uniqid(md5(rand()), true) . '.jpg';
		$this->_resizeImage($image,  $tmpfile, 8, 8, 100);
		$this->_grayScaleImage($tmpfile);
 
		$a = array();
		for($i=0; $i<8; $i++)
		{
			for($j=0; $j<8; $j++)
			{
				$rgb = $this->_getPixelValue($tmpfile, $i, $j);
				$a[] = $rgb['r'];
			}
		}
		$avrg = (int)(array_sum($a) / count($a));
 
		$s = '';
		foreach ($a as $value)
		{
			$s .= ($value > $avrg ? '0' : '1');
		}
		unlink($tmpfile);
 
		return $s;
	}
 
	public function getDistance($image1, $image2)
	{
		$bits1 = $this->_getChainOfBits($image1);
		$bits2 = $this->_getChainOfBits($image2);
 
		$distance = 0;
		for($i=0; $i<64; $i++)
		{
			$bit1 = $bits1[$i];
			$bit2 = $bits2[$i];
 
			if ( $bit1 != $bit2 )
			{
				$distance++;
			}
		}
 
		return $distance;
	}
}
 
 
$hamming = new Hamming();
$distance = $hamming->getDistance('image-1.jpg', 'image-2.jpg');
 
echo $distance;