//process image before uploading to server
function process_image($source_url, $destination_url, $quality){
    $info = getimagesize($source_url);
    if ($info['mime'] == 'image/jpeg'){
      $image = imagecreatefromjpeg($source_url);
    }
    elseif ($info['mime'] == 'image/png'){
      $image = imagecreatefrompng($source_url);
    }
    imagejpeg($image, $destination_url, $quality);
    return $destination_url;
}