Comparar 2 imágenes para saber si son diferentes

[webseficientes]

mmm, filesize no funciona con urls.

aca encontre una funcion donde compara el header Content-Length

function remotefsize($url) {
$sch = parse_url($url, PHP_URL_SCHEME);
if (($sch != "http") && ($sch != "https") && ($sch != "ftp") && ($sch != "ftps")) {
return false;
}
if (($sch == "http") || ($sch == "https")) {
$headers = get_headers($url, 1);
if ((!array_key_exists("Content-Length", $headers))) { return false; }
return $headers["Content-Length"];
}
if (($sch == "ftp") || ($sch == "ftps")) {
$server = parse_url($url, PHP_URL_HOST);
$port = parse_url($url, PHP_URL_PORT);
$path = parse_url($url, PHP_URL_PATH);
$user = parse_url($url, PHP_URL_USER);
$pass = parse_url($url, PHP_URL_PASS);
if ((!$server) || (!$path)) { return false; }
if (!$port) { $port = 21; }
if (!$user) { $user = "anonymous"; }
if (!$pass) { $pass = "phpos@"; }
switch ($sch) {
case "ftp":
$ftpid = ftp_connect($server, $port);
break;
case "ftps":
$ftpid = ftp_ssl_connect($server, $port);
break;
}
if (!$ftpid) { return false; }
$login = ftp_login($ftpid, $user, $pass);
if (!$login) { return false; }
$ftpsize = ftp_size($ftpid, $path);
ftp_close($ftpid);
if ($ftpsize == -1) { return false; }
return $ftpsize;
}
}