class ImageHash {

    const FILE_NOT_FOUND = '-1';

    const FILE_EXTNAME_ILLEGAL = '-2';

    private function __construct() {}

    public static function run($src1, $src2) {

        static $self;

        if(!$self) $self = new static;

        if(!is_file($src1) || !is_file($src2)) exit(self::FILE_NOT_FOUND);

        $hash1 = $self->getHashValue($src1);

        $hash2 = $self->getHashValue($src2);

        if(strlen($hash1) !== strlen($hash2)) return false;

        $count = 0;

        $len = strlen($hash1);

        for($i = 0; $i < $len; $i++) if($hash1[$i] !== $hash2[$i]) $count++;

        return $count <= 10 ? true : false;

    }

    public function getImage($file) {

        $extname = pathinfo($file, PATHINFO_EXTENSION);

        if(!in_array($extname, ['jpg','jpeg','png','gif'])) exit(self::FILE_EXTNAME_ILLEGAL);

        $img = call_user_func('imagecreatefrom'. ( $extname == 'jpg' ? 'jpeg' : $extname ) , $file);

        return $img;

    }

    public function getHashValue($file) {

        $w = 8;

        $h = 8;

        $img = imagecreatetruecolor($w, $h);

        list($src_w, $src_h) = getimagesize($file);

        $src = $this->getImage($file);

        imagecopyresampled($img, $src, 0, 0, 0, 0, $w, $h, $src_w, $src_h);

        imagedestroy($src);

        $total = 0;

        $array = array();

        for( $y = 0; $y < $h; $y++) {

            for ($x = 0; $x < $w; $x++) {

                $gray = (imagecolorat($img, $x, $y) >> 8) & 0xFF;

                if(!isset($array[$y])) $array[$y] = array();

                $array[$y][$x] = $gray;

                $total += $gray;

            }

        }

        imagedestroy($img);

        $average = intval($total / ($w * $h * 2));

        $hash = '';

        for($y = 0; $y < $h; $y++) {

            for($x = 0; $x < $w; $x++) {

                $hash .= ($array[$y][$x] >= $average) ? '1' : '0';

            }

        }

        var_dump($hash);

        return $hash;

    }

}

var_dump(ImageHash::run('1.jpg', '2.jpg'));