Legality of Screenshots/Concept art

[Bond]

I should preface this by saying my knowledge of the law is currently limited to a business law class I am taking; however, I could fully answer this question in three years.

There's four main considerations when assessing whether use of a copyrighted work is "fair use," these are, in no particular order:

1. The purpose and character of the use - i.e. how much are you changing the copyrighted work from its original state? is this for commercial purposes? (significantly altering the work and commercial motive will not fall under fair use)

2. The nature of the copyrighted work

3. The amount and substantiality of the copyrighted work used

4. Effect of use upon the potential market for the copyrighted work - i.e. if the use adversely affects the market value for the copyrighted work it is unlikely to fall under fair use

So, your two main issues are probably going to be how substantially are you altering the copyrighted work(s) and is this for a commercial purpose? Hope that helps.