Paint can as a camera invention

I was recently at the National Maritime Museum and saw in the shop a paint can that had been modified into a pinhole camera. Here it is -- with the patent number given near the bottom as (American) patent 6618556.

The patent's title is Chemically resistant pinhole camera. It is an ingenious example of recycling, and it works
by as the patent summary explains "The inner surface of the camera is coated with a chemically resistant light absorbing material such as a black epoxy paint. The inner surface also forms a curved image plane to support the photographic material."

Below is the main drawing for it.

I love it when apparently simple new products have patent numbers on them, so that people can learn how they work.. in this case, with 18 pages of information.

There is a website for those who want to buy one.