remote file Is ımage or not ımage?

function isImage($url = '') {
    if (!strstr($url,'http')) return false;

    $ch = curl_init($url);
    curl_setopt($ch, CURLOPT_NOBODY, 1);
    curl_setopt($ch, CURLOPT_HEADER, 0);
    curl_setopt($ch, CURLOPT_MAXREDIRS, 3);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, 0);
    curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, 0);
    curl_setopt($ch, CURLOPT_FOLLOWLOCATION, 1);
    curl_setopt($ch,CURLOPT_CONNECTTIMEOUT ,5);
    curl_setopt($ch,CURLOPT_TIMEOUT, 15);
    curl_exec($ch);
    $contentType = curl_getinfo($ch, CURLINFO_CONTENT_TYPE);
    curl_close($ch);
    if (strstr($contentType,'image') || strstr($contentType,'octet-stream')) return true;
    return false;
}