Customize the watermark module

I was wondering if someone would have an interest in doing some customization to the watermark module for me. I need to give a user the ability to overlay an image on top of another and then have the module save as a new image in 4x8 size or "4000 x 1000" pixels. It would be a module to offer customers the ability to take an image from an album, choose from a stored library of xmas card templates, and then after they choose the template would overlay their image. They could then save it as a new image that is the pixels dimensions listed above which equals to a 4" x 8" 250 dpi print. Please let me know if this can be done and how long it would take. I would be willing to barter prints for you. I own a digital printing lab.

Jeff