Hi,
I agree with Ticknall , I also think it is the same person taken at different times in their life.
The picture on the left (or top) looks older by a couple of years. Eyebrows change - she probably started plucking them when she got older as a lot of women do. Nose change - the younger woman has her head/face slightly tilted upward - while the older one is looking at the camera at a very level postion. I don't think a nose would look exactly the same in two photos if the heads are in a different angle as these photos are . It's very hard to tell if it's the same person or not the same person when they are taken at different angles. I never look the same person in a lot of my own photos myself.
Regarding the "mother" and "aunty Gladys" wording under the pictures , do you know if the album changed hands in the family? Say for instance the album was not originally your grandmother's album but it was her first cousins album which later got passed onto your grandmother for some reason, maybe her first cousin died so she inherited her album -And then your grandmother added photos to it too.
Is the handwriting on both pictures written in the same style as each other, written by the same person? If not it may explain why one photo says aunty and the other says mother. It still doesn't explain why she is called Gladys though of course, if you can't find a sister of your grandmother's mum with the name Gladys - unless it's your grandmother's first cousin's (on your grandmothers father's side ) mum and the first cousin wrote the word mother - then on the other photo your grandmother wrote "aunty". Maybe check your grandmother's father's family too to see if her father had a sister called Gladys. Just some totally wild thoughts for you.
Another thought; Is the wording written on the pages of the album or the photo's themselves? If it's on the pages, perhaps the photo's have been taken out of the album at some point in time and then put back in their wrong position.
If It's not the same person, they almost look like identical twins to me. They look so very,very alike to me
