We always used to dress up at Christmas, Easter and Whit Sunday,to go to the threatre, to have our photos taken (in a studio), etc. but how many people bother to do that now. As 2c says, I think people had a lot of self pride in the 19th century (and early 20th century) and would certainly have dressed up for photographs.
Lizzie
ps. Lydart - I love the photo of your granny