A function to know if a given image is animated

gistfile1.php

// See http://stackoverflow.com/a/415942
function is_animated_image($filename) {
  if (!($fh = @fopen($filename, 'rb'))) {
    return false;
  }

  $count = 0;
  // an animated gif contains multiple "frames", with each frame having a
  // header made up of:
  // * a static 4-byte sequence (\x00\x21\xF9\x04)
  // * 4 variable bytes
  // * a static 2-byte sequence (\x00\x2C)

  // We read through the file til we reach the end of the file, or we've found
  // at least 2 frame headers
  while (!feof($fh) && $count < 2) {
    $chunk = fread($fh, 1024 * 100); //read 100kb at a time
    $count += preg_match_all('#\x00\x21\xF9\x04.{4}\x00\x2C#s', $chunk, $matches);
  }

  fclose($fh);
  return $count > 1;
}