Sharing revenue

[onpelikan]

I have a shop with T-Shirts and other goods with pictures. The pictures are made by my friends or collaborators. Revenue from one thing is 10% for them. I would like to automate the process of calculating and paying their share. Everything should be associated with the author of the picture and the shop will show me how much many I should pay them based on sales. Or better send money via bank account monthly :-).
Do you have an idea of how to do that? Is there any module?
Thank you very much.