Stock models are boring.
Sure, she's pretty or he's handsome and yes, they have white, even teeth and shiny hair. But what's that got to do with the pigmentation problem your patient is facing?
Stock models are not a good choice because they take away the proof you're trying to create.
You've heard people say, "sell the promise" - well, that stock model is not the promise.
Use your patients as models. You can hire them to come in for a photo session and get real people who've had real stuff done. Show THAT as the promise. Although many of these same patients won't ever allow before and after photos, that's not the point.
The payback can be huge. A professional photo that shows the positive emotions experienced because of the treatments they've had with you is priceless.
Plus, anyone who is on a website as a model will be talking it up. It's personal referral on steroids.