Here is the original:
You can see that most of the photo has faded except the edges, as they were hidden behind the frame over the years.
I started by making a feathered selection around the faded area. I adjusted the levels, manually corrected the color balance in the shadows/midrange/highlights, adjusted the levels again and then did some minor touch up with the spot healing tool.
The result isn't perfect, but good enough. :)
It's much easier work when the original hasn't been in the sun: