Before I begin - Nothing in this answer shall be considered legal advice and no attorney-client relationship has been established (taken from GDSE's snippet topic).
I think the first thing to mention is that it's unlikely to come to any lawsuit. Unless the project becomes a massive success (either commercially or otherwise), then the company will most likely focus their lawyers on other projects (especially if they're in-house lawyers, because they're stretched across the whole company). That being said, it's not impossible, so I advise caution in this situation. If you're completing work for a client, I suggest that answers contained in this question may help: How to handle client requests to violate copyrights? . As @Laurenz mentioned before, if you can, use non-copyrighted work in the public domain.
To answer your question in more detail however, I did find a good post in another forum (emphasis all mine) (source: http://ask.metafilter.com/130670/Is-including-a-movie-poster-image-in-a-blog-legal - I suggest taking a read of the actual post in the format of the forum itself as I am unable to include more than two links with my small reputation over here; I've copied the main body of the text over here regardless for posterity.): "I'm not an attorney, but I do have both a personal and professional interest in copyright law. First, the DVD cover, movie poster, screencaps, etc., are all copyrighted. With a few exceptions: anything from before 1923 is in the public domain in the US, so if you're working with those you're OK. (That's for the thing itself you're looking at: a new DVD cover created in 2000 for a movie which was originally released in 1920 is still copyrighted.) At some times copyright renewal was required, so for some older works if the copyright wasn't renewed it might have fallen into the public domain, but that's hard to determine. But for any relatively recent movies, yes, they're copyrighted.
That said, you might be able to use covers/posters/screencaps under fair use. However, fair use is a very grey area of the law, and there's no way to know for sure whether use of copyrighted material falls under fair use or not, short of an actual lawsuit where the judge makes the ultimate determination of whether a use falls under fair use or not. There are guidelines for fair use, namely the four factors judges are expected to consider in determining whether a use is fair use or not,
but it's not as simple as adding up how many factors fall in your favor and how many fall against you. Anyone who tells you they have a black-and-white test for determining whether a given use qualifies as fair use or not, short of actually bringing the matter before a judge in a lawsuit, does not know what they are talking about. However, in your case many elements would be in your favor: you're using the material for criticism; I assume you're not profiting yourself from your posts (if you are, that's less good for you); your use is unlikely to harm sales of the work; and for the screencaps at least, you're reproducing only a very small portion of the movie.
Now, as a practical matter, it seems that studios don't care too much about enforcing copyright against people using covers, posters, or a small number of screencaps as illustrations in works about a movie. And even if they do, as long as it's just a smallish blog and not a money-making venture, at worst you're likely to get a cease and desist (C&D) notice from the studio ("this infringes our copyright, please remove it"), in which case you remove it, and everyone's happy. Assuming you promptly remove anything for which you do receive a C&D notice, you're highly unlikely to face a lawsuit."
The later half of the post drifts slightly away from this topic in that it talks about blogs. Nevertheless, this situation is similar still: most of these designs will be small enough that they fall under fair use. If they are used commercially or if they are used in a situation where they gain a large view count (i.e. perhaps a charity webpage, which isn't commerical, but is run similar to a company), then the fair use system is much more likely to no longer apply. As the poster says - without the matter being taken to a court, there is no courtlaw on the matter to form a legal basis from.