跪求PHP图片加水印和压缩的代码，万分感谢

<?php    

    header ("Content-Type: image/png");    

        

    $markImage = imageCreateFromPNG('logo.png');    

    $srcImage = imageCreateFromPNG('back.png');    

        

    imagealphablending($srcImage, true);    

    //关键代码, 透明图片    

        

    $markW = imagesx($markImage);    

    $markH = imagesy($markImage);    

        

    imageCopy($srcImage, $markImage, 180, 30, 0, 0, $markW, $markH);    

    imageJpeg($srcImage);   //output to browser    

        

    imagedestroy($srcImage);    

    imagedestroy($markImage);    

?>