Can you protect images with transparent gif in Gallery

Hi there, I know that adding a watermark can be done with phpThumb, however, I want to incorporate with Gallery. I’ve trawled around to see if there is a way to either add a watermark or replace an image with a transparent gif if its right clicked on without much success.

Does anyone have a solution?

It may be quite a straightforward job but I can’t seem to find an answer anywhere.

Thanks