The fact that you need to store all previous blocks (and content) to fully validate later blocks is an advantage in this case.

I was super into using hashcash for antiabuse in social stuff pre-bitcoin, but the difference in hashing rate in-browser versus in C even then rendered it somewhat ineffective at anti spam as an abuser could hash 10-100x faster, and the delays on the UX side for legitimate users made it a nonstarter. With GPUs and hashing asics now that gap is even worse.

(FWIW these days the Steem blockchain that holds the steemit content is delegated proof of stake, for block production.)

How does Steem store user generated content like images and videos? Are they in the blockchain itself? If so, how do they solve the problem of people downloading the blockchain being liable for illegal content added by other users?

The Steem blockchain only holds unicode text: words, html, json. Images and video are embeds or img tags, which point to URLs on ipfs or elsewhere. That’s a separate challenge.

It seems like any on-chain user generated content is likely to be a problem; arbitrary binary data can be encoded as text. I suspect this problem already exits on the bitcoin chain though, so it's not like it's unique to Steem.

Not sure what they do, but it's entirely possible to build a solution where all image/video content is stored on-blockchain as well.

>If so, how do they solve the problem of people downloading the blockchain being liable for illegal content added by other users?

Divide each file into N shards, make sure every miner has no more than N/2 shards of any file at any point in time. You only 'get' a complete file if you specifically ask for it.

I'm not a lawyer, but I believe it is unlikely this solution will hold up in court.