Parental internet filtering software that can block specific content rather than just whole domain names

All of the parental inteet filtering software I'm aware of seems to be based around blocking entire domain names. So that's an easy problem to solve.

However I'm trying to find inteet filtering software that will have the awareness/database to block specific non-kid-friendly pages or images without blocking entire domain names.

For example blocking the user from accessing gruesome images/content on Wikipedia, but not blocking the whole site.

There's only a few ways I can think of that this software would work:

1. Artificial-intelligence (for images at least). I don't think we're quite at this stage? At least for something easy to install at home.
2. So I'm assuming this would need to work similar to web-browser ad-blockers... users submit URL rules for specific offending images/pages, and the software still allows access to anything else on the domain by default. Obviously po sites etc would still just block the whole domain.
3. Text based filtering of words (I'm aware that some programs do this already).

I think what I'm really after here is #2 above. Does such software exist in the form of browser plugins or Windows applications?

Also I'm aware that any system can be easily gotten around by a number of methods. My client here is more looking to protect their kids from accidentally coming across things rather than doing so intentionally.