https://browser.dataspace.copernicus.eu/ Sentinel 2 imagery is the closest thing to an open source spy satellite

https://earthexplorer.usgs.gov/ has a ton of aerial photography across the US. satellite pics too, but the planes are usually higher res and cover more area

Well, weather satellite images are generally considered to be public domain and pretty easy to receive, so if it fits your use case, get yourself an SDR dongle and an appropriate aerial and start collecting them as they go past

Might find yourself with a new hobby after

OpenArealMap

What type of imagery are you looking for? I typically use NASA or ESA unless I need something very specific, and those tend to be closed-source.

I use gee as the access point by and large. GOES or something like cfsv2 or gedi I’ll download directly because I have to.