…because if they didn’t, they’d simply wander off immediately, and not stand in place and remain looking at you, at least until the shutter snaps. No?
My cats know, because whatever cute pose they’re in, they will change (if not run away entirely) before I can get my phone out and the camera app loaded.
That’s why I wait until they’re sleeping.
Heh, my brother had a dog that would run and hide if you even started to point a camera at her. I bet she was on the lam.
When my brother’s children were very small, we were constantly taking their photo, as you might expect. His dog, a White West Highland Terrier, would sit down directly in front of the children, assuming that you wanted her in the picture.
Our senior cat got very tired of being photographed not long after we adopted her, and will leave promptly if she sees a camera (even a phone) aimed in her direction. Our junior cat is a bit more cooperative with being photographed.
Proof.
Mine, canine and feline, have always been most likely to come towards the person holding the camera, resulting in a picture of Nose.
I don’t think they’re noticing the camera at all; I think they’re noticing that the human holding the camera is focusing on them, and conclude that the human therefore is likely to be willing to give them some pats.
The Siamese are like vampires.
Or smoke.
As soon as I think I’ve gotten a picture. Poof…gone.
I’d swear they don’t exist til the howling starts.
The dogs are always moving too much. Blurs. Or butt pix. Which are cute, sometimes.
I’m not really that fast anymore. But I keep trying.
Don’t know if my late beloved Blackjack* could recognize a camera but if knew someone was looking at him he strike his show dog pose. He’d do it in front of other dogs too. One time wife and i were sitting on bench waiting for a ferry to come in. A woman came down the street walking her little female Spaniel. Blackjack struck his pose and she had to drag her little dog away. That sweet little thing looked like a cartoon dog with stars in her eyes and her little dog heart popping in and out of her chest.
*Best dog ever. I have proof.
The one on the arm of the chair is totally smiling!
Not only that, sometimes they’ll photo-bomb the picture! And this isn’t even a cat or dog! 
We were just saying the other night how funny it was that our shih tzu always seemed to strike a pose or put on a face when a camera was on him. I miss him so much!
Our first dog, the BC, could “work” a camera better than most children. When it was just my wife and I (and K9) at the beginning of our marriage, we had a camera that had the sonar focus feature and we wanted a pic of the three of us so I put the camera on the roof of the car and aimed it at the bench in front of our apartment. Set it for 20 seconds and us humans got behind the bench and BC (I swear) hopped up onto the bench, parked her butt in the seat snd looked straight into the camera. Perfect picture. I have to assume she “heard” the sonar from the camera and focused on that.
Yeah, the dog I grew up with in the 50s was the OG photobomber. We’d never notice her maneuvering into a shot until we got the pic developed. Shiny green eyes!
I’m reading a whole lot of “my dog posed!” and “my dog photo bombs” and “cute butt pics” and yet - other than the curled-up ball of kitteh, and the gopher (?) adorableness - I’m seeing a distinct lack of photographic evidence.
Okay, the kitten posing on the arm of the chair is pretty stinkin’ cute, but thay doesn’t count, cuz it’s a kitten, and by definition, weapons-grade cyooooote.