This sounds too complicated, I think I’ll just stick to covering every hotel mirror in a thick layer of mustard, it’s much easier.

Just poke it and see if your finger touches, or if there’s a gap to determine whether the surface is reflecting, or the back of the glass is reflecting.

I found a YouTube link in your post. Here are links to the same video on alternative frontends that protect your privacy:

• yewtu.be
• inv.nadeko.net
• yt.artemislena.eu
• piped.video