You may have missed what abduraooft was indicating:
5.3.0 Pixelation support (IMG_FILTER_PIXELATE) was added.
5.2.5 Alpha support for IMG_FILTER_COLORIZE was added.
IMG_FILTER_PIXELATE is not available for you to use, and IMG_FILTER_COLORIZE *may* be available depending on your revision (you only have 5.2 here, you need 5.2.5 to use IMG_FILTER_COLORIZE).
Since none of these exist, PHP's default fallback on undefined constants is to treat them as strings. This is why you are getting the error; IMG_FILTER_PIXELATE is interpreted as 'IMG_FILTER_PIXELATE' instead of as its intended integer value.
As of PHP 5.5, the MySQL library has been officially deprecated. It is recommended to move to either MySQLi or PDO libraries for your mysql connectivity. See here for help choosing which interface you prefer: http://php.net/manual/en/mysqlinfo.api.choosing.php