Hi Kernow,
I've taken pictures as both hand luggage and checked luggage before, without issue. The maximum size will be the standard 56cm x 45cm. Anything bigger will need to be checked luggage - lots of bubble wrap is the order of the day here, but I can confirm that the staff at T1 (when I last tried it!) were very helpful indeed, and the pics arrived intact.
Cheers,
Chris.