Yes, It is both a dumb image and I was able to Re-create the PCB from it.
If you do: Gerbview / File / Export to Pcbnew and choose the right layers (there was no layer info in that old project), then KiCad is smart enough to make copper tracks from the straight line segments on the copper layers.
KiCad also has the built in functionality that if a footprint is placed on a piece of track that does not belong to any net, then it assigns the net from the pins of the footprint.
So you do a bit of cleanup from the Gerber import (It had a lot of “painted pads” which I all deleted, and then placed imported footprints from Eeschema on the track ends. (By snapping a pin of a footprint to the endpoint of an existing track). And then KiCad gives net names to all the tracks that get connected to all the pins of that footprint. Those “dumb images” have quite a lot of info in them:
- PCB outline.
- All track segment locations.
- Footprint locations, implicitly in the pads and/or end of track locations.
- Mounting hole locations and sizes.
Layers as Soldermask and Silkscreen are also easily recognizable from the sort of graphics they have.
Inner layers do usually not have footprints, while the outer two layers do. If you accidentally swap top and bottom layer, then a lot of the SMT parts won’t fit because the footprint is mirrored.
A quick search:
https://html.duckduckgo.com/html?q=altium+gerber+file+naming+convention
And then the first result:
And you have some info about the naming convention altium uses for it’s gerber files.