That's awesome! My Grandad used to draw pictures like that on the edge of books when I was a kid, not as intricate as those one's though, but it was something I had long forgotten about until I saw that, so thanks for sharing, and reviving those memories of my Grandad.
I love it! Some people are so creative. Here's one of my students paintings. He's got a sense of humor. LOLOLOL Look close...little surprises everywhere.