Well, this is embarrassing.
I took the car to the shop, the shop took the wheels off, examined the rotors as bed they could and could not find any cracks. They did say there was a small lip at the edge of the braking surface and they believed the position of the flash created a shadow that looked like there was a crack. He said they could replace the disks and pads if I wanted, but there wasn't a reason to. I said, okay, I won't.
When I got the car back, I tried the flash experiment: one pic with the flash above the lens and one pic with the flash below the lens. See if you can figure out which is which.
I've been a customer of this shop for a few years now and will continue to be.