使用PHP为AWS S3桶中包含的图像添加水印

是否可以在使用PHP存储的AWS S3 Bucket上应用水印?

我已经尝试了以下检索图像是否存在，水印应用后。

    $galleryImg = '_1473241284.jpg';
    // echo $galleryImg;
    test(file_exists('https://s3-ap-southeast-1.amazonaws.com/bucketname/test123/'.$galleryImg));
    //for direct apply watermark on server
    if(file_exists('https://s3-ap-southeast-1.amazonaws.com/bucketname/test123/'.$galleryImg)){
    // test("hiii");
    // echo "hii";
    $watermark->apply('https://s3-ap-southeast-1.amazonaws.com/bucketname/test123/'.$galleryImg, 'https://s3-ap-southeast-1.amazonaws.com/bucketname/test123/'.$galleryImg, $watermarkImg, 3);
    $response1 = $client->putObject(array('Bucket' => BUCKETNAME, 'Key' => 'bucketname/test123/'.$galleryImg, 'SourceFile' => 'https://s3-ap-southeast-1.amazonaws.com/bucketname/test123/'.$galleryImg, 'ACL' => 'public-read'));
    //echo "watermark applied";
    }