Navigation using photos. Did not like existing apps, so made an app that lets you match a photo to an (OpenStreetMap.org) background map, and shows your position on that photo during your trip.

Works great with physical maps, screenshots of maps or downloaded pictures of maps. NavigateAnyMap.eu (Android only, sorry!)

Free as in beer, will tell you is uses ads, but have not added them yet (and will make a paid, non-ads version first).