Deny the usage of animated avatars

[iblis]

Could you guys try the following code, and report back bugs if there are any?
This snipplet detects if an avatar is animated (or any other .gif)

PHP Code:

function isAnimated($filename)
{
    $fp = fopen($filename, "rb");
    $whole = fread($fp, filesize($filename));
    $i = -1;
    while($i = strpos($whole, 0x2C, $i+1))
    {
        if(strpos($whole, 0x00, $i-1) == $i-1)
            $c++;
    }
    if($c > 1)
        return true;
    return false;
}