I checked it out, and tbh I think that the post requirements are pretty restrictive, especially considering that Lemmy is relatively new and doesn’t yet have a critical mass of contributing users.
Assuming that the axiom that states that only about 10-20% of users actually post is true, you’re already facing an uphill battle in terms of growing your subscriber base. On top of that, the community theme (art with no context) sounds like an interesting endeavor, but it’s also pretty niche. It’s gonna be hard to find the community organically. Or for your community to find you, organically.
Also, by requiring that the post be a non-flash photograph of the work of art as displayed, you’ve placed additional barriers in front of those 10-20% of content contributors. I mean, how often does the average person go to the museum? Also, does the poster have to have taken the image themselves, or is finding and posting an image you found online (that is a non-flash photo of an artwork as-is and adheres to the community rules and post guidelines) acceptable? The last sentence that reads, “Mods reserve the right to ask where you’ve taken the photo of the art.” seems to imply that the image in the post needs to have been taken by the person posting it.
I enjoy the premise/theme of the community, but I feel that you’re either going to have to lower the barrier to participate/contribute, or you’re going to just have to accept that it’s gonna take a fair amount of time before your community grows into a self-sustaining body. It’s like you’re taking care of a newborn pet, and, at least in the beginning, you’re gonna have to feed your community/pet with fresh posts pretty often. You’re also probably going to have to advertise your community when it’s relevant.
Remember that at the start, even Reddit went out of their way to populate their front page with posts from various dummy accounts to create the illusion of activity. Anyway, best of luck with your community, I sincerely hope you’re able to retain and grow the community you’re looking for.