It seems a good work, well done!

Feel free to steal the code of this add-on and use it at your wish... Me too I don't have any spare time ;)

Can you tell me if there is a reason this solution would not work today?

I downloaded your attachment and installed it, first uninstalling the old one, and I don't see a difference. It still brings up the ver 1 of the reCaptcha.

Any ideas for me, other than getting my client to just let me bring him onto the ver. 8 platform of Concrete5. ;-)

For me the v2-version attached in the original post above works with current 5.6.3.5 without problems.

Did you register and use the recaptcha v2 Keys athttps://www.google.com/recaptcha/... ?
Did you set the new credentials in the recaptcha app settings?

Thanks for your response. Yes, it works fine. I eventually discovered that the add-on, Extended Form, that I was using had it's own embedded reCAPTCHA code using v1, so it was not using the updated reCAPTCHA addon. If fooled me for a bit. After replacing it with the core's form block it worked perfectly. The one thing left that is throwing me is how to change the text that displays above the captcha that says "Please type the letters and numbers shown in the image." which obviously no longer applies. I have found it embedded in a couple of different captcha.php files and changed it, but they must not be the right ones because it doesn't change anything in my page. If you have any clues for me there I'd love to hear them.

UPDATE: I found the location for the text I needed to change. It was in the package folder for recaptcha at /packages/recaptcha/models/system/captcha/types/recaptcha/controller.php

I copied it to /blocks/recaptcha/models/system/captcha/types/recaptcha/controller.php and edited the text to my preference.

I should have easily guessed this earlier but sometimes I get tunnel vision following other suggestions instead of thinking for myself. :-)

Thank you! I am using extended form as well, and this helped me resolve the expired v1 issue. v2 now working great.