yep Steen2 is correct
you would have to call thier agent ..pay a fortune in fees and you would still be told No unless it was for advertising something like pepsi.
The pics you see around are ususally stolen,taken from mags etc and the posters and users have not had permission in most cases to use them.
Before you think of doing the same ....consider if you could afford a lawsuit just in case the celeb decides to sue you ,if you can afford it go ahead...but my guess is you cant ,so l would avoid that type of business plan
Hope that helps