If I had to guess:
1. CP - image uploads and decentralized platforms that are intentionally hard to censor don't mix very well
2. Storage space - megs and gigs don't grow on trees yo
pretty much these
also text is better!
Imageboards are nice for threads about anime girls or tv shows i guess, but do they really contribute much to discussion? (reaction faces don't count)
People already are more than comfortable linking to music, videos, articles, games, software, etc; it just doubles duties for an imageboard operator to host discussion as well as image uploads.
Personally feel "danbooru" type imageboards are seriously underappreciated; they are way better ways to find art relating to a character or show or meme, etc than browsing a thread catalog. Am I weird for thinking so? Some programmers stress using the right tool for the right job ...
If other people handle image hosting, it relieves a textboard operator of a number of potential penalties / costs (liabilities) like >>2 said.
Sure, people can still post credit card numbers and links to CP torrents, but that's more manageable than people using your systems to upload CP to the public
... and there's nothing stopping you from extending multich API and adding image uploads / thumbnails either (public domain software with an IRC room and "meta" board in the software itself). It would be incredibly trivial to have a multich board that detects an Imgur URL to automatically embed a thumbnail with a link to the image -- same as how many *ch sites will embed a YouTube thumbnail/embed -- plenty of solutions to allow people to share multimedia with less stress on a server operator, admonishments of hotlinking be damned!
> there's nothing stopping you from extending multich API and adding image uploads / thumbnails either (public domain software with an IRC room and "meta" board in the software itself).
also modified viewer.py and settings.py
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