It’s not sexist, it’s threatening.
While you may mean well, the vast majority of times a woman is complemented by an acquaintance or stranger, it’s because that person is trying to hit on the woman.
You might think “shouldn’t that be flattering?” No, it really isn’t. Every single woman I know has countless stories about how they have been harassed by desperate men trying to get into their pants. If you could barely walk into a public place without random strangers harassing you, you’d be soured on the idea too. To further compound the problem, men are on average bigger, stronger, and more aggressive than women.
So as an example, I was out with my girlfriend once, walking down a crowded street. There was a group of people we had to walk around so we went single file. In less than 30 seconds, she already had some shitty man cat calling her with loaded compliments. I shoved some people aside to make sure I was standing next to her again and he shut up immediately. This is just a fact of life for most women.
Men may not understand this because they only very rarely receive random compliments, but it hits very different as a woman.
There is an appropriate time to compliment women, and it’s after you have already built up a trusting friendship. Besides, a compliment means more coming from a friend than a stranger.
Bet you could hack one of these together with a Raspberry Pi plus camera module. Not exactly a low effort project though.