Ask HN: Possible startup idea, mobile ad network with captchas?

I just wanted to put this idea out there for discussion.

Would a mobile ad network startup work if it ran ads in apps, and if clicked, the user has to fill in a captcha, and only then would the clicker get through, and only then would the advertiser pay.

The first question is, why would I run these ads?

Could there be a much smaller amount that's paid on the click, then the remainder paid on entering of the captcha?

I could see the startup that implements this doing well because why would advertisers want to advertise anywhere else? And once this startup has all the advertisers, do publishers have any other option than to use the service?