Contributed by Howard: "This photo was taken at Penrith Speedway, New South Wales, Australia, probably in the late 1920s or early 1930s"
The Norton is a 490cc OHV Model 34, easily identified by the 4-speed gearbox and the final drive on the right hand side of the machine. The half round shape of the oiltank suggests a 1928 model. The front forks are sidespring Druids, one would expect Webbs.
Compare the motorcycle to this one