There are rulings around concerning thoroughbred breeding in the context of hobby vs business (and this is an industry where a yearling can sell for $1m) - I can't remember the details, but it revolves around
proving you are a business. This can include a business plan, a significant proportion of of personal income being derived from the business, employing others, a business name, premises. Although I have no problem proving that we are a cattle business, our horse breeding is still treated as a hobby - in spite of receiving over $60k for horses sold (you don't want to know about the costs though
) I'd expect proving you have a photography business has parallel requirements.
As kiwi says, talk to an accountant - but kiwi's $20k seems a viable benchmark. Remember, this is billings - it is NOT earnings, as costs have not been taken into account. (Now, this gives me an idea ... a photography
tax dodge managed investment scheme for high earners. Who wants a D3x for their holiday snaps... 49% off...
)
The hobbyist issue here is not about "devaluing the industry" or "stealing from professionals" (or even "tax evasion") - it is straight (or arguably convoluted) accountancy and tax law that applies across a range of industries. Don't confuse the ATO's view of "hobbyist", be it photographer, horse breeder or whatever who still sells things deliberately, and the more generic hobbyist or amateur who does it for fun, and a sale is a bonus.
The issue that the photography industry has to face up to the fact that it has low barriers to entry and a lot of willing participants. If some of those competitors are "hobbyists" (in an amateur sense), the "professionals" will have to recognise that there is more than providing an image, and instead start to provide what "hobbyists" can't - professionalism, reliability, consistency, attention to detail, marketing - and work at retaining their clientele.