Not as much effort as you might think. Command-line rendering of html (including css and js) and taking a screenshot is not very difficult. If a site used this

Not as much effort as you might think. Command-line rendering of html (including css and js) and taking a screenshot is not very difficult. If a site used this method, and someone is highly motivated to break that captcha, the effort put in would be nothing compared to the benefit of bypassing the "security".