wtm2 will have difficultie ratings. The simplest way to judge difficulty is by the number of people who solved a shot in a given timeframe. Assuming a 30 day timeframe (which is exactly how long you are able to solve a movie right now) where do you think we should put the limits?
Are you able to extract the distribution of the number of people who solved each of the last month movies (about 800) ? Then you can find for example how many people solved the 20% more difficult (hard), the 20% easier (easy) and the 60% remaining (medium). If you send me the data I can do the job.
There's no way to create an universal difficulty rating because difficulty is completely individual.
If you know the movie by heart it's easy to solve it even if only 3 other people have solved it so far. And conversely, if you haven't seen the movie it may be hard to solve it even if it's a blockbuster solved by 300 players.
But you might be able to calculate a personal difficulty rating for a still. But even that would be quite a complex statistical endeavor.
@biglebowski we are of course aware, that calulating the difficultiy for a specific user is very complex but this is also not what we are looking for. We are looking for the average user. We will still be off quite a bit for some people but "easy" should be easier than "hard".