I know there are many threads already on this topic but nothing helped me.
I've set reCaptcha for comments in my "Category blog" of K2, but the image does not appear. Only words appear that "Enter the two words you see below". Made all necessary setting in "parameters" in tabs "comments" and "advanced". Entered public and private key from google reCaptcha.
I'll be very thankful if you guide me step by step. Thanks...

Hi. Try to:

1. Check your page for Javascript errors.
2. Use another browser.
3. Update your K2 installation to the current stable version.

Thanks. Updating k2 solved the problem.

You are welcome.