People should not post many stills from the same movie at the same time.
It's stupid to publish them all together so someone will have to make a choice and this choice should be made by the submitter. If you have different shots of a movie, pick the one you think would be best on the site (not the hardest one btw, since most of the time if you have made 10 shots from a movie you know it inside out, but not everyone does so pick a reasonable one) and post only that one.

Also try not to post consecutive screenshots of movies that are clearly connected (like 5 consecutive shots from Hitchcock movies) because these would normally appear consecutively in on the site. If you have many from the same director (or similarly linked) try to post them separately (with a few days interval in between). Otherwise we'll have to accept only one (and again, the moderators will have to make a choice, and if they don't agree many screenshots might be published consecutively which is silly).