None of the cats I had so far in my house, both my own cats and the foster cats, have ever paid attention to their image in the mirror. They have all just ignored it, as if nothing was there.
I know people whose cats get crazy and charge the mirror, or yell or hiss at the image.
Somewehere I had read that the kind of reaction a cat has towards their own image reflected in a mirror is an indicator of their smartness, intelligence. The article said that the smarter they are, the lesser their reaction will be, that is they know they are themselves. Dumber cats do not recognize themselves and hiss. This is what the article said.
Casper, pretty much, ignores his own reflection but, when he hears his own voice in a recording, he comes to investigate.
A while back, I made a video of Casper scuffling with another cat, from outside, through the patio screen door. When he heard himself, growling and snarling through the TV, he started looking around to find the interloper.
Maybe most of our cats don't care about their own reflection in a mirror but these "cats" didn't:
Sweetie has gone to the Rainbow Bridge now but he used to come into the bathroom and stand on the vanity and look at his reflection in the mirror. He was never upset at seeing that other cat looking back at him so I think he understood mirrors too.