So I showed my mum the photos I'd found under my bed. Some of them I'd correctly inferred the basic contents, but the details were interesting, as was her "wow" on some of them. The best "wow" was on the long rolled up school photo, which she like me thinks will have her mother in it, which seems to date from 1928. However, she also expects that it will have my grandmother's cousin Majorie in it, and my mum is going to visit Majorie soon, so we hope that Majorie will still recognise them both from then. Slightly younger was a photo of 3 women outside a church - they are Majorie, Josie and another cousin, who were the bridesmaids at my grandmother's wedding in 1940. (Jean Kathleen Clarke married William Douglas Rennie in 1940 in Hull - Google doesn't know that yet...)
Other little details emerged. There were a group of pictures that I'd correctly inferred were of the house she lived in in St Albans. But they're far more fun when she pointed at the car in front of the house and said "That's the car I learned to drive in."
However the photos that had the most "wow" for me were some of a wedding. It's Josie's wedding to Peter Simpson, and there's this rosy cheeked little bridesmaid in several. "That's me, aged 4" said my mum, proudly. "Don't I look like Erin?" [my niece]. Maybe she does, but she also looks very very like the picture of my sister when she was young.