As others mentioned, the geoguessr community has a lot of resources, but it's largely focused on locations on streets (cause the game is built on Google streetview). Things like streetsigns can really help narrow down a country.
As someone else mentioned, Open Source Intelligence (OSInt) is what you want to be looking for. Investigative journalism sites like Bellingcat actually show their work, which is really cool. For example, they wanted to find the location of a massacre in ethiopia, so they used an app called Peak Visor to match the topology of the mountains in the background to triangulate the position. There's also tools to use the angle of shadows and things like that. They have tutorials on their site.