I'm not convinced it is a valuable problem that needs solving.
If you really want a web which only humans can browse and which prevents non-human-operated clients from visiting websites, require a submission of a blood, hair and urine sample or a photocopy of the person's driving license or something.
Until that point, computers will want to do useful things on behalf of humans, so it might be best to not get in their way because someone told you to on a website.
For some companies though, it's about protecting IP, e.g.
* Google wants to stop scraping so that you can't build a competing search engine that just scrapes Google for every search term that you see.
* LinkedIn has an amazing database of user information, you wouldn't want someone scraping all of it and creating LinkedIn2.
* One of the reasons Quora exists is that there are a lot of opportunities in mining the answers; they don't want another company to get to piggy-back on their hard work creating the site, acquiring users, making a good UI, paying for hosting etc.
Nobody "told" me to go solve this problem, nor do I have any interest in implementing a potential solution; I just thought it was interesting. Because it was interesting.
If you really want a web which only humans can browse and which prevents non-human-operated clients from visiting websites, require a submission of a blood, hair and urine sample or a photocopy of the person's driving license or something.
Until that point, computers will want to do useful things on behalf of humans, so it might be best to not get in their way because someone told you to on a website.