Geograph
From OpenStreetMap Wiki
Geograph British Isles is a UK photographic project using Ordnance Survey maps and producing Creative Commons photos.
Geograph in OSM
Freemap displays geograph images on an OSM map
OSM in Geograph
They currently use Ordnance Survey maps on the website and for locating photos (so their geolocations database may be derived from OS) They are also sponsored by Ordnance Survey, and so presumably get the nice normally-not-free maps for free. All in all geograph are unlikely to be switching to OSM any time soon, although some of the geograph developers are big OpenStreetMap fans [1]
