I know it sounds really plain and easy, but since you have photo shop, design your watermark there, save it to your computer, and then just pull up your photos and drop the transparency on your design. That's how I used to do it.
to design watermarks , you can try this imaging sdk which contains such a function. it can be applied in c#, vb,etc. Install it and it becomes a selectable processing option.Then you can create and edit watermarks in any program at all, including Adobe Acrobat . Just open the images, select watermark ,and follow the setps given in the sdk, the task will be finished in several seconds.you can then zoom in and zoom out , or adjust the light of the watermark on your own will. if you haven´t found a good choice , you can have a try. best wishes.
