@dansup A federated community is only as good as the moderators who put in the work. I expect folks who host or join Pixelfed to share images aren't motivated to moderate content and delete spam accounts.
If you don't deal decisively with the spammers, they will consume you. Some sort of built-in spammer check is a good start. Account creation doesn't have to be immediate.
[Take this advice from someone who was on the Internet when it was just engineers, scientists, and academics].