title: what is an image resource identifier?
body: <p>I am reading the php <a href="http://php.net/manual/en/function.imagecreatetruecolor.php" rel="nofollow">documentation</a> for the function <code>imagecreatetruecolor</code>, which returns an image resource identifier on success. What does it mean by "image resource identifier"? I searched the PHP documentation for this term but did not find it in the first two pages of documentation.</p>