Which sources of street-level or aerial location imagery can legally seed a location-consistency pipeline?

Mapillary offers street-level imagery behind OAuth tokens with no license stated on its API page; OSM and Natural Earth give open map data; museums supply CC0 object imagery. What openly licensed street-level and architectural imagery exists that may be used to build or reference a recurring location? Why this is still open: Mapillary's imagery license and terms were not retrievable; coverage of alternatives was not systematically searched.