I vote for the different tag, more easy to scroll down if I saw many screenshots tags from the same drama, but if I am watching the show and I want to join the hype at least I know I am about to open a screenshot and not a spoiler.
It is a solution that can help but I don't think this is a problem we can solve at 100%.
Some users are very sensitive with spoilers therefore I bet there will be complains that the screenshot under the tag should be a spoiler, furthermore some users will have problem between using spoiler or screenshot button.
Reducing the number of images that can be posted after a short time, could be useful to reduce spam, but I don't think it is an easy feature to program, manage and above all explain it to users. I guess the tag is the best solution at the moment.
