I use Photoshop to make the watermark logo, but then my gallery automatically embeds the watermark when I upload them. You can still do it manually in Photoshop. Just create a layer on top of the photo and place or create your logo there. You can choose teh opacity should you decide you want it transparent or not.
Good job Tim! Pretty cool pics. I have read about that method before, but never had the chance to give it a try. It's a pretty good idea.