Partial answer to
Are pictures taken from ISS geolocalized?
Yes, if the astronauts keep the clocks inside the DSLRs set properly (and I'm guessing that they will definitely do this!) then the location of the camera can be reconstructed easily. What the camera is pointing at is a different question. The camera can be virtually geotagged, but not the subject.
GPS inside the ISS
I'm pretty sure that it's going to be extremely difficult for a commercial GPS unit inside a handheld camera held by hand inside of a big tin can (Faraday cage) called the ISS will pick up enough signals from enough GPS signals at any given moment for that unit to register a fix.
It might happen once in a while, but not in a regular, reliable way.
Yes answers to Does GPS work at ISS? and other GPS Q&A here indicate that the beam patterns from some GPS satellites intentionally cover an area slightly larger than earth and so there's an annulus around Earth's disk as seen from space where bright "flashes" of GPS signals will appear.
However there are several differences between GPS positioning by a spacecraft and by a simple commercial hand-held device.
Commercial units have firmware restrictions on both altitude and speed to make them COSPAR-friendly.
Commercial units require simultaneous captures of at least four satellites to get a meaningful position from space, (if they weren't self-blocking for reasons described above). Fancy space GPS can play tricks and record fixes from different GPS satellites at different times and reconstruct a trajectory with an orbit ephemeris and them back-calculate a position at a given epoch. DSLRs can't do that.
This would require the camera "seeing" all around the edge of the Earth's apparent terminator, which means you might have to hold the camera in very specific positions fairly close to the cupola's central window. The signals come from all around the edge of the huge looming Earth disk, not from the ground.
...is there a software which converts pictures timestamps to space localization?
I'm no expert, but I assume that ISS photographers keep the clocks in the cameras set properly. The orbital history of the ISS is well known and documented, so all it takes is reading the timestamp in a given historical image's metadata and some historical TLEs and one can find the position of the camera to a few kilometers.
What the camera is pointing at is a different question. The camera can be virtually geotagged, but not the subject.