as far as I know, the licensing of unreal includes a clause for vfx/machinima/movies which says you can create renderings, even commercial ones without the usual 5?% fee... but simply check out the license for yourself.
anyway, I have to ask... why in the hell would you want to do that?

take max, maya, blender or whatever and render your images there... realtime engines heavily limit your available featureset, need way more complex setups even for simple objects, etc.. it simply makes no sense to me.