In the picture is a girl with her sister. They had a tradition to take pictures on every first day of school and this photo is one of the examples. Preferably with a black skirt and white shirt look. They, pupils, wouldn't wear this combination day to day, but it was an unquestionable outfit for certain occasions, such as the first day of the classes, official meetings, and formal events devoted to for example, New Year, Mothers Day, etc. Perhaps not much has changed today.
As for the picture itself, in the late 90s more and more families started having their own cameras, they'd take pictures and develop at special places. They have a big box of printed photos from that era. But before that, there were men with cameras at certain spots they would visit, they would take pictures and hand developed versions a few minutes later. They had horses (such as in this picture), cars, sometimes real dogs. You could find some of these men with photo cameras outdoors - nearby metros, Zoo, circus … But some of them had their own studios, with nicely decorated walls.
They stopped visiting them once they got their own camera in the late 90s and she cannot remember when was the last time she saw those photographers.