I've also really liked this image. The old grizzled veteran and his wife.
I think the wife is wearing her best (looks to be a paisley patterned shawl) and is almost smiling (not common at that time as it was a serious matter to go get your photo taken).
The Paisley design first appeared around 200AD in Persia - during the 1600s the Paisley pattern started to appear on shawls imported by the East India Company. In the 1800s the weavers in the town of Paisley, Scotland became the primary producers of the pattern due to their skill in producing the design in more than two colours.
The wife's shawl looks to be more than a two colour design - probably a very expensive item at the time.
The old man is wearing his best - albeit well worn and obviously old at that time - but still wearing a jacket with waistcoat and a chain . No doubt a timepiece in there somewhere. The medal doesn't seem to be attached to the chain but has not just been pinned onto the overcoat - it may be pinned to the jacket/waistcoat and then folded onto the coat just before the picture was taken. No idea why the overcoat and shawl were not taken off. Maybe it was cold, or maybe the wife wanted her bonnet and shawl to be in the photo.
But I still can't pinpoint the medal. The clasps do definitely look to be a MGSM with 6 clasps. But the medal and hanging bar just isn't quite right. And I can't really see the Queen's head there - although I remember reading that at some time the medals were worn differently - ie displaying what we would now call the reverse.
So I gave up checking all the medals I could think of and settled on the MGSM:
Maybe one of us will find it, thanks all, Steve