There actually are some people doing tags like that. Not a huge market, but people do show interest due to the novelty. I didn't bother to bookmark the sites I saw last year, sorry.

I tinkered with a SS tag and thermark and engraved a headshot photo of my dog on one side and the vital stats & med needs on the other. People who see it love it and want one, but rarely want to pay the photo editing fee, nor do they want a generic image, because it's not "their dog." It's not a market I push at all. There are a gazillion pet tag places on the internet selling for $2-$5 and I don't need to be one of them!

Michel