Photoshop

During the Cold War the US needed high-quality images of Eastern Bloc military to assess the threat from the Warsaw Pact. Billions were poured in to higher and higher quality spy satellites, but the film canisters from the cameras still needed to re-enter the atmosphere, be rescued in the air from their parachutes (I'll bet that was a fun piloting job) and processed. Presumably The Russkies did the same.

There was only so much post-processing chemicals and the human eye could do to improve the quality of those photographs but increasing computer power and the rise of the CCD allowed digital scanning of the negatives, then Top Secret computer-based editing software was developed by the military to enhance the results. The satellites went digital and the pictures were simply transmitted, so no more air-rescued canisters.
This all trickled down to the consumer arena in the form of Adobe Photoshop and its imitators, and these were game-changing: the digital darkroom had arrived.

Photoshop remains the premiere image editing tool. Even in its "Elements" (simplified and cheap) versions, it is possible to rescue and improve images that would simply not have been possible when we all wore rubber gloves and had stinky chemical baths in darkened or red-lit rooms.
I use it in repair mode - colour balance, exposure changes, rotating, cropping, invisible mending, removal of unsightly wires, drainpipes, girlfriends etc...
What it is amazing at is panoramas: take 8 or 9 sequential negatives and sellotape the prints together. The exposures will be  inconsistent, the edges won't match and the whole shebang will be rubbish.
Do the same in Photoshop and with a bit of fiddling you'll get a seamless panorama, exposure-corrected, images matched and adjusted and how the eye saw it at the moment of exposure. Pure magic and hugely satisfying, especially on old, prized negatives.