Personally I agree to the fullest that all uploads should have screenshots. I know that the reason some auto uploads do not have screenshots is to avoid the risk of having spoilers in the screenshots (as a bot doesnt know the difference) but I do think manual uploaders should take the time to make a few screenshots so that we can see the quality.
Using a player like VLC makes it really easy to make screenshots. You can download VLC player here:
http://www.videolan.org/ it is free and plays all videofiles and more, no codes needed.
To make a screenshot in VLC player:
Play your video file with VLC player. Take a screenshot by pressing the Shift + S. You may also pause your video at a selected point and press Shift + S to create a screenshot.
The screenshots are usually saved in your normal Image folder location.