Hints for this game:
Doing research online is perfectly acceptable. If you recognize an actor or actress, checking their filmography on wikipedia or imdb can help.
Don't bother doing a reverse lookup search for any of these. I make all of the screen caps from my own digital video collection, and I use drag and drop to insert them to posts.
The more obscure the screen cap appears to be on first glance, the more likely it is to be from a movie which many people would watch more than once.
Every screen cap is very carefully chosen by me. I'm hoping that ALL of them can be correctly identified.
There are intentionally different levels of difficulty, but the sequence of posts is entirely random.
Your gut feeling answer is probably going to be correct, more often than not.
Ask yourself: Why did onomatopoeia choose THIS screen cap? There is always a reason. Don't just look at the pics; study them.