129. Stock Photos – stock photos like the ones you find on this website and many others, are licensed and bought from online stock photo marketplaces.
The owner of the photo (usually the photographer who took it) receives income each time his photo is re-used. A portfolio of thousands of commercially-useful photos can generate a decent monthly income stream.
Photographers generally aren’t looking to sell this zero effort recurring income stream, but sometimes you will see photo rights come up for sale in a bankruptcy or an estate settlement.