How stable would the various colors of ink needed for pictures be? I suppose you could also print out a separate B/W version of each color channel for later reconstruction.
Maybe you could print out a color calibration strip with known values, and then use that as a benchmark so you could reverse fading via software? Kind of like what NASA/JPL does so they can color-correct photos taken by planetary landers.
(I know that this isn't what the OP meant, but it's interesting to try and mitigate the limitations of the more common backup solution -- i.e., just printing the photos themselves).
