What is the best and fastest way to check if the image is valid in PHP?

Question

What is the best and fastest way to check if the image is valid in PHP ? I need it to be able to check GIF, JPG as well as PNG images.

Answer 1

I use this function... it checks urls too

function isImage($url){
   $params = array('http' => array(
                'method' => 'HEAD'
             ));
   $ctx = stream_context_create($params);
   $fp = @fopen($url, 'rb', false, $ctx);
   if (!$fp) 
      return false;  // Problem with url

  $meta = stream_get_meta_data($fp);
  if ($meta === false){
      fclose($fp);
      return false;  // Problem reading data from url
  }
 }