I stumbled into this idea by accident. My grandma had hundreds of old photos of our town from the 1940s and 50s. I scanned them all and started posting them on a local history Facebook group. People loved them. Eventually I set up a simple website with print-on-demand options for high-resolution copies. It's not quitting my day job money but it brings in a few hundred dollars each month and was mostly set-and-forget after the initial scanning.