The first link, "Flo Control" (named after Flo the cat) was built in the late 1990's, and this link on MetaFilter (https://www.metafilter.com/15802/) is from 2002, but the host link appears to be dead.
The OP is kinda swatting a fly with a sledgehammer, but blindfolded, because the system would probably break if the door changed or someone moved something into the detection window. Problem with CNNs is training them to know what is NOT a valid condition, and that is VERY VERY HARD.
Thanks for finding that! I forgot about the wayback machine. I also forgot that is what websites looked like in the late 90's. /r/blunderyearsforwebsites
Here are two others, using different tech to automatically open the door for the pet.
Facial recognition: https://www.hackster.io/windowsiot/cat-door-with-pet-recogni...
Pattern recognition: https://hackaday.com/2010/05/14/cat-door-unlocks-via-facial-...