plone.formwidget.captcha is a z3c.form captcha widget for use with Plone. It is a z3c.form re-implementation of the collective.captcha package written by Martijn Pieters.
Add the following code to your buildout.cfg to install plone.formwidget.captcha:
[buildout] ... eggs = ... plone.formwidget.captcha ... ... [instance] ... zcml = ... plone.formwidget.captcha ...
A view to generate a captcha image and/or wav file, and to verify user input against it.
A cookie is used to transfer state from one request to the next. The state is used, together with a server-side secret, to create a random string of characters, which in turn is displayed as a captcha image, or transformed to an audio file. Verification happens case-insensitively.
Note that the captcha 'word' is only usable for 5-10 minutes, after which the view will not accept it any more. Moreover, a different word will be generated for a given session key every 5 minutes.
This makes these captchas replayable for up to 10 minutes if a determined user keeps sending the same session id. Because of the server-secret though, captchas are not transferrable between sites.