This comment is why I came to comment myself. You cannot remove these types of things once they are baked in they are there for good unless there is some very complex math involved in somehow safely removing or flagging this section of the blockchain but then that would defeat the purpose of the whole cryptographically secure nature of it.

Second is you can stomp down on websites that search the blockchain for text, images, videos, illegal documents, etc. However that is not solving the issue directly. However that is hurting a lot of positive potentially interesting uses on account of the very small percentage of abuses. What you essentially have is a GIANT public whiteboard but you've given everyone a permanent marker. If you can control the content that goes in very directly (doing some AI analysis on photos for example) then there will always be a subversive tactic like the XOR one mentioned above, etc.

I suppose the real reason I comment here is that I cannot forsee anyway that these things will not happen and will not continue to happen. Like with ThePirateBay I suppose you have to go after the sites that make it convenient to find this information rather than trying to solve the problem in the blockchain itself _somehow_, which I think we can pretty much agree from a security standpoint and tech-forward approach would render the whole concept of blockchain dubious.