Banner Generator - Preferably already written but modifiable

I need the ability to provide a free banner generator to our free members to use for promotional purposes. (static banners only w/ 2-3 lines of text and a watermark Also need a premium banner generator that would include all the bells and whistles in banner creation for the paid members to generate their own banners. There are many scripts of this type on the market, but I need to have the ability to have someone modify the source code to suit my purposes as needed. If you have already written this type of script, that would be best, to shorten the development curve, delivery timeline.