A Challenge, A Task

For those of you who hate having to enter a five-letter sequence of characters to post your blog comments:

If a form is as the bottom of a page, wouldn't a user have to scroll down to submit that form? If a field has no focus, doesn't the user have to either click that field or tab over to it? If a form has fields hidden from view in a browser, will it not be blank?

Why doesn't someone create a system that uses metrics of human-browsing behavior to determine of a post is spam or not? If 99% of 10,000 visitors had to scroll down, give focus to the fields, and entered values only in text fields that are visible (i.e., don't have an extra div cleverly hiding them from human-view), then it's safe to assume those 99% are human. If, on the other hand, a request is made, a response is posted, but there is no intermediate activity (scrolling, focus, gradual field-value change, pauses, etc), and fields which shouldn't be visible are filled out, isn't it safe to assume that the post should be marked as spam?

I'm just saying... Someone should make this thing. Yes, it involves several components, but it'd be damn cool.


Thoughts?