Here's a case in point. A German film called An Unusual Affair. https://www.gaytorrent.ru/details.php?id=148073
Not slacking the uploader at all. But the images of the posters are practically the same. And no thumbnails! I have the file (may not be exactly the same) so I could provide the thumbnail but the image slots is already full.
It's an okay movie. Eye-opening for housewives or the bi-curious married guys.
I didn't say thumbnails is needed for a torrent description. I said a good thumbnail must be a part of the images uploaded for the post.
Nobody wants microscopic thumbnails. And yet some people upload them to get seed points. 
Which I don't.
I have no problem if the torrent uploader posted his own thumbnails or images. Uploaders gets respect, thanks and seedpoints for uploading. Those who upload inappropriate images should be spanked.
I have no problem with high resolution images of the movie/file. All I'm saying is that for one torrent, there has to be at least ONE good thumbnail.
Basically I agree that Mods don't have time to micromanage. That's fine. So I suggest this. If a user can upload a good thumbnail but the "Upload image" option is greyed out because it is filled with posters/stills of the file/movie, the user can contact Mods and the mod can free up one image so that the user can upload the thumbnail. Vice versa, if the Mods sees a torrent full of posters/stills but no thumbnail, the mod can free up a slot.
It's harder to quantify what is a "good" thumbnail. I would say that anything below 30 minutes, a 1/2-minute setting would be "good". For a movie that's over 60 minutes, a 3-5 setting would be "good". And of course, no damn microscopic thumbnails.
Some torrent posts (from all genres) have individual still photos of the video but not thumbnails. But because the post had so many stills, users who have downloaded the torrent cannot upload the actual thumbnail for the video.
This is not much of a problem with regards to porn videos but for films, sometime the stills are the same posters in different resolutions. And for movies, you don't need so many posters or DVD covers too. For some porn posts which had multiple video files, this is also a problem because one file is for one specific scene only.
The system should be changed to allow at least one thumbnail (with info such as resolution, audio and video codec, running time) be in the post. Otherwise, people have to download the torrent just to see their effort is wasted.