Inspired by this I took a couple pictures, such as a picture of me with their textbook to work out my height, for pupils to iterate this idea of scale. What I really wanted was to find a picture of a claw scratch on a door, but I think that what I did find is even better.
An online news article was talking about a big cat that was spotted in the rural village of Thrupp. It was sighted many times but there was no evidence of it till someone took this picture:
Its a great picture for scale and we had plenty of animated class discussion speculating on the size of the cat. What was great about this is that we could confirm the actual size as the cat was later caught on camera: