May I use your image

There are times when I ask people if I can use their images for my art work. How it works for me and the person I am collaborating with is that once I have finished my work with their image I email it back to them in high res and ask them to post it on RedBubbe for 50% mark up as well as I do the same, so that myself or the other person own the art equally and we both have a chance to make a profit of the finished piece. If you were someone who is willing to let me use any of your images , feel free to comment here and let me know.