The examples:

https://www.dangermouse.net/esoteric/piet/samples.html

The last one is astonishing: "Okay, this one is really wild. Piet J. (yes, that's his real name) was browsing art in a small gallery and saw a work which reminded him of a Piet program. He spoke to the artist, who claimed to know nothing about the language. Piet took a photo of the artwork (left), converted it into a clean image file using close colours from the Piet palette (right), and tried running it.

It ran!..."