I held a lesson for 7th graders on vector graphics and...

The PCs in the classroom had a system where the teacher can lock all student computers to force them to concentrate on the teaching. Locking them disables the mouse and keyboard and the screen displays a small logo of the program (NetOp) which is basically a lock on a white background.

I had a bit of spare time before the lesson and noticed that it's possible to change the bitmap image that's displayed when the screens are locked. Guess what I changed it to?

Yes!

It was a huge success!