User blog comment:Kirkburn/Technical Update: February 10, 2015/@comment-5558012-20150210212412/@comment-126761-20150211152350

As already linked in the blog post, the new version of reCAPTCHA does not use images (except as a fallback): http://googleonlinesecurity.blogspot.co.uk/2014/12/are-you-robot-introducing-no-captcha.html