It is interesting that you think none of your ancestors were involved in the military in Aus. That might well be the case, though, it is very interesting for me as my dad and I have just this year rediscovered a family collection of over 700 photo's and there are some real gems in the collection, however some of the men are not individuals associated with the family. One amazing little picture has the very tantalising words written on the back;
"Mary
......d you the love of Jimmy
......n't show it to any one"
Mary is possibly one of two we know of in the family....... long since deceased, but the man in the picture even my Gt Aunt who is 91 doesn't know, or she claims not to know as one Mary was her mother and the other her sister! I would say by the apparel the chap is wearing and the seeming age of the picture it is most likely to be my Gt Aunts mother who received the picture. So what Mary was getting up to I don't know, so it may well be that the picture is of relevance more to a female than a male in your family. In another branch of my family a Gt Aunt was very much involved with an Italian POW called Silvio, I have managed to gather together scraps of information and bring them together, and if I understand the Italian writing correctly I believe Silvio and my Gt Aunt Marjorie would have married, but it never happened as he went back to Rome after the war (WW2). She never did marry.
I love finding out these tidbits of info, just a shame no-one is left to be able to ask outright what was going on........ though they would probably have told fibs........
Philip