750 ml bottle in a picture to avoid sharing. Boo....
Bill Valvanis has a great series of pictures of a maple every couple of years with sons from 4 or 5 to present day, or at least close to that when I was last there. The sons were late 20s. It shows the tree getting older very effectively. You could pick something that changes to take the pictures with - a dog, a similar tree in the ground, sitting on the hood of different cars, different 750ml bottles,...
On a shorter time scale, a picture in spring with background trees starting to leaf out, summer, fall, winter covered with snow.