Protect part of a page with Captcha

Hello

I have been asked to protect part of the content of a page with a Captcha. I am trying to protect a page and not a form. I do not necessarily want people to register on my site, just to create a small hurdle to discourage spammers.

The system would probably work through the use of conditional shortcodes much like is done in several membership systems, only people would not be forced to create a username/password. I have thought of the possibility of using some kind of default guest username/password activated by visiting a specific page (not quite sure how to do this yet) but I do not much like the idea. Of course, as the purpose of the captcha is not to prevent access but simply to (slightly?) reduce the interest of the site to spammers etc., maybe the solution is simply not to have any protection at all.

I would appreciate any thoughts.
Andrew