Categories (even the primary ones) change as people vote for categories. The more votes a category gets, the more likely it is to become visible as a category. The category which receives the most votes after a certain point becomes the primary category.

what about a collection of photos? compilation set of photos is it ok?

If you copy the DVD content files (VOB files) on your hard drive and you can open them without issue, it should be fine. As long as you can read them on your computer without the original DVD inside, it should be good for anyone. I don't think porn DVD were protected, from what I remember. Can you tell more about your process? If I understand correctly, you create images of DVD (>> .iso or .img files) then you mount them later and play them with the player of your choice, right? (because in this process, the image could be encrypted anyway, the player will decrypt it. But I'm not entirely sure. I always used DVD ripper softwares)

I wasn't looking at the date so I apologise but since I already wrote my post I believe it won't hurt anyone to read it (especially those who are beginners)