Well, my camera sucks so I don't think it'd show up even on a picture. The vet had to angle a light just right to see the indention. It kinda just looks like a fuzzy white-ish crease...
I use a digitatl temp. and humidity gage inside the tank to take humidity readings. I'm pretty sure it's taking the readings on the warm side of her tank, though her water bowl is on the cool side (if that helps). It's not a huge tub though...