Ask Lemmygrad

They don't sell their labour [power], they sell the product of their labour; as a result, assuming they don't employ anyone (or use contract labour), they are artisans, a fairly small but distinct class that shares traits with both the proletariat and the petite bourgeoisie.

Actually, wouldn't this make them an artisan? Not proletarian because they own the tools they use to do their work, but not bourgeois because they also don't exploit any workers other than themselves.

But they have control over where and when their labor power is utilized, which is what makes their situation different.

This is a good question, thanks for asking it. It makes me realize there is more of a spectrum between lumpenproletariat and monopoly capitalist, although there are actors that are very clearly in one category, there are areas where it blends. And of course it's always in flux.

They sell the output of their labour, not the right to use their labour for a day/week/month at the going rate for labour power (the average cost to reproduce a worker plus maybe some bonus pay for scarcer labour skills or a bribe for being a labour overseer).

In the one case, the service of photography is being sold at the going rate for photography and no surplus value is extracted from the labour. In the other case labour power itself is purchased, and the capitalist is now responsible for extracting as much useful input as possible from the labourer during the time they've purchased the labour. In that way they can profit from surplus value produced in excess of the cost they paid for the labour power.