Check Remote File

With CURL

function checkRemoteFile($url) {
    $ch = curl_init();
    curl_setopt($ch, CURLOPT_URL,$url);
    // Don't download content
    curl_setopt($ch, CURLOPT_NOBODY, 1);
    curl_setopt($ch, CURLOPT_FAILONERROR, 1);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
    if(curl_exec($ch)!==FALSE) {
        return true;
    } else{
        return false;
    }
}

Without CURL

function is_webfile($webfile) {
    $fp = @fopen($webfile, "r");
    if ($fp !== false) {
        fclose($fp);
        return true;
    } else {
        return false;
    }
}