@dilemmax Take a look at "Auto Movie Thumbnailer," at https://funk.eu/amt/. The user interface is a bit clunky, but it will do a bunch of thumbnail sheets at once. I have it installed on a Windows 10 machine, and it passed all of my computer's multiple virus checks. I don't think there's a Mac version, but I haven't looked closely.

@leeniedo That's good now. I always wondered why random photos were attached to some torrents. I didn't know you can get seed points for doing that.