Thank you for making it your browser startpage, that's flattering!
Regarding the previous discussions, for now I'd like to try having only the artwork and the discussion for the current day. It goes against what most content platforms are proposing today with all the unlimited feeds everywhere but I feel it's a good way for people to take the time to reflect on the artwork and get deeper conversations.
All the previous comments are stored in a db at the moment so if the community grows and would like to access the previous discussions, that's feasible.
Regarding the spam issue, posting a comment currently requires creating an account (although without any email verification afterwards at the moment for the HN launch as I know many people here can be held back from trying out when the signup process is too intrusive).
There's also a minimum word limit for the comments to encourage constructive discussions and not just comments of the type - "Nice colours", "Love it", "That's not art".
Finally, I hope that being quite niche to art lovers, that might prevent too many spammy comments. We'll see!