The picture has a possibility of being faked. The photographer, J. Ross Baughman, took three then and still famous photos of Rhodesian Security Forces torturing blacks and then won a Pulitzer Prize for those pictures. However, both other photographers in-country and the Rhodesian government disputed Baughman's written description of the photos, how Baughman took the photos, and the photos' authenticity. A General Manager at the Associated Press also called bull.
J. Ross Baughman - Wikipedia
Edit: I do have a book on the Grey's Scouts by Alexandre Binda and I recall the book taking the position that the pictures were fake. I also recall Ian McCollum and Larry Vickers stating that the short shorts had left Rhodesian service by the tail end of the Brush War, which would be around 1977 when the photos were released. However, nothing was very consistent in Rhodesian military equipment issuance and the Grey's were a special operations unit.