The oldest photo I have is of my 3xgreat grandparents with my 2x great grandmother as a child, taken 1871 in Dundee. However I do have a slightly later photo, a quite worn tin type from the 1880's, which shows my 4xg grandmother (lived 1817-1906), which generationally speaking trumps the earlier one!
Actually reading the other posts here I realise I am relatively lucky, going through my tree I have
6 out of my 8 great grandparents
9 out of my 16 2xgreat grandparents
6 out of my 32 3xgreat grandparents
1 out of my 64 4xgreat grandparents
The last of my 5xg grandparents died in 1884, the last of my 6xgreats died in 1869, so I suppose it is not theoretically impossible that one day I may even get further back, but given a choice though I'd rather find photos of the 2 missing great grandparents , but not complaining, as I say consider myself lucky to have as many as I do, and blessed to have been able to share them with wider family across the world.
EDIT:
Here are the photos in question:
This is the oldest, 1871, Dundee, (It was coloured by a clever soul on one of these boards, I couldn't do it being colour blind, but looks great to me). The little girl with the Celtic Cross round her kneck is my g-g granny Holohan. The standing man, and the seated lady his hand is resting on my are my 3x g grandparents. They were both born in Ireland, he lost both parents, her her father in the Great Famine, when they were both barely teenagers. Her mother took him in as an orphan, and being forcibly evicted from their home, bought the family to Dundee, where they later fell in love and married.
This is the tin type taken around 1884. Sadly by time I inherited it it was already a century old, and very badly damaged as you can see. Nevertheless the little boy at the front is g-g grandad, the couple at back his parents, my 3xgreat grandparents, the lady sitting centre my 4 x great grandmother.
She was born in a sleepy picture postcard Essex country village 1817, and married at 22 to a farm worker from the neighbouring village, John aged 26. When she was nearly 40, they upped sticks and moved to London, West Ham. The Royal Victoria Docks had opened that year and John obviously felt he could make a better living as a docker there. It was a bad move as he was dead within 9 months of scarlet fever, probably picked up in the more crowded urban living conditions. She was left in a new home with 5 children to bring up alone, aged 14 years - 18 months, which she did working as a monthly nurse to local wealthy families, before eventually being taken in and cared for as a 'virtuous widow' in the West Ham Widows Alms Houses, and where she lived for over 30 years. These were next to West Ham Parish Church, the spire of which can just be seen in the photo (if you squint!), so this was no doubt then taken on a family day out, a picnic maybe, in West Ham Park, probably by a photo vender.
Despite the extreme damage I still feel lucky indeed to have it.