These photos seem to represent the same man. He appears wearing a pith helmet in the Middle East, which means he would have embarked with the 6th Field Ambulance there, and later moved to France/Belgium. He might have moved on to the 12th Field Ambulance, but this isn't clear. In the bottom photo he is wearing a German helmet and greatcoat.
I have created a commemorative online database of the WW1 volunteers of Essendon and Flemington in Victoria, with a blog to support the website: see link below.
I have other websites and blogs which follow other interests.