Legality of Sharing Movie Screencaps?

I print "three-sided cards", usually on 4″×6″ paper. Some of these are photos I take, some are art public domain art, some come from anime imageboards.

One thing I found was that a clean frame of 720p or better video makes a great print so I have a series of cards that come from movies and TV. I don't sell the cards so I think these fall under "fair use"

https://tinytake.com/screen-capture-copyright-violation-or-f...

However, this academic asked the studios for permission to reproduce a frame from a movie from a book and they were told "no"

https://eve.gd/2015/05/12/another-copyright-absurdity-using-...

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