Are all the users around the same age?
The pictures indicate: 20-30 average. Some a bit older.
Why does everybody make a series of photo’s?
The pictures show they try out different poses/close ups.
What is the influence of the background (different picture style)?
The people don’t interact with the background (only on last picture?). Just the end result (pictures) are looking different.
Do they make pictures to look back at it again later?
The pictures do not seem to be made to have an overview. It just the fun of making pictures and try out what you can do to make a funny picture.
Are some pictures unnecessary to keep?
Second colum, last row. Nobody would like such a picture i guess.