you may edit and publish images you've created yourself - and that includes photographs - but you can't use someone else's work without their agreement. Even if you get a copyright release, it's almost certain to contain a clause that prohibits any alteration to the original image.
The famous person doesn't have a say in the matter either way - unless the alterations you make could be considered to be defamatory, in whch case you may be on the receiving end of a 'cease and desist' letter, or in extreme cases an action for damages. That's a very remote possibility however, unless the changes you make to the image show the person in a compromising situation, one that would damage his/her's reputation in the eyes of the public, or cause distress to his/her family.
As for photoshopping pictures of famous people, Iv always been against it as well as being famous they are just like us in many ways imagine if someone got a picture of yourself and photoshopped it for all to see,
And made money from it?
There are many other ways of making money from photography and photo manipulation as quite a few artists do it and are quite succesfull at it too.
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