It would need to be JavaScript or jQuery of some sort. I’m not sure exactly how your script would interface with reCAPTCHA, but it would somehow detect a successful input and then display the email. How securely you want to obscure the email determines how the email is stored in script to begin with. If this is to merely hide addresses from automatic email scrapers, a simple assembly of parts would be adequate. Some sort of simple cipher will stop all bots and most inquisitive humans. For maximum security, get the address from the server via Ajax. Anything sent with the original page prior to successful reCAPTCHA response can be eventually decoded by anyone determined enough.
If your intent is to merely stop email scrapers, reCAPTCHA is overkill. AFAIK scrapers do not interpret JavaScript, so running a replacement script on page load should be adequate. Or present the email as an image. Bots do not run OCR either.
