Captchas only let you verify that the user is human, this API lets you do more: it lets you verify that your web application is going to run unmodified and that

Captchas only let you verify that the user is human, this API lets you do more: it lets you verify that your web application is going to run unmodified and that the user is going to see what you want him to see, _everything_ that you want him to see and nothing else. Unlike captchas with this you can remove adblockers, greasemonkey/stylus edits, extensions adding download links to your youtube videos, etc, from the picture.