$myImage = new GD::Image(100,100);
        ... various drawing stuff ...
        $redImage = new GD::Image(50,50);
        ... more drawing stuff ...
        # copy a 25x25 pixel region from $srcImage to
        # the rectangle starting at (10,10) in $myImage, merging 50%
        $myImage->copyMerge($srcImage,10,10,0,0,25,25,50);