Perhaps I had better remove the 'Completed Thanks', as JJ and I have been exchanging PMs (and I mean messages not post-mortems

) on this baby all afternoon

The conclusion we are arriving at is that it is indeed a post-mortem picture and I think the baby's eyes are open rather than painted on the lids as there is a very hollow, ill look to the eyes. Presumably had they been painted, they would have been made to look healthier.
The census records for what I think is this family do not indicate any children died between 1871 and 1881 but there is quite a large gap between the birth dates of my grandfather and his 2 older sisters, which could indicate the death of a sibling.
Thanks so much, Carolyn, for the added colour - much appreciated
Maggie