This is high on my wish list as well. I might take a crack at this when I get a chance. From looking over the templates, I don't think it's too bad for a piefed-only version, but it would be my first time messing with the database structure for piefed and the stakes are higher than tweaking css or an html template.
In essence, it would just need to create a label that causes post images to blur (like nsfw or nsfl posts do depending on your settings). Then, when you go to create a post, it would be a box you tick, just like creating an nsfw post.
Because of federation, it would be nice if a piefed community mod could assign it to posts that federate in from platforms that don't support it. However, much like post flair, that would not federate out to other piefed instances if the community home instance isn't piefed.