Postcard-backed photographs of individuals and groups were popular from the early part of the twentieth century up until the Second World War. They provided a convenient way of passing photographs to family members and friends. However, not all were posted. Some bore a brief annotation showing who the subject of the photograph was – an undoubted plus for the 21st century genealogist.
In this case, the indidual who made the inscription obviously wanted to make clear who was not a member of the family:
Ma & Dad and Family with exception of the soldier and the chap next to him.
The photograph on the front of this postcard may be seen here. I have to say, though, with an inscription like that on the back of the photograph, it does make you wonder why the poor soldier and the chap next to him were even invited to joing the group