<fb:captcha/>
An element within <form/>
tags, this
tag places a “reCAPTCHA” image within the form that contains two pieces of text that
must be entered into a text input by the user. The form gets
redirected back to the URL in the action
parameter for the form with the additional parameter
fb_sig_captcha_grade
appended, which lets your
app know whether the CAPTCHA entry was successful.
As a developer, you can feel proud to include reCAPTCHAs in your apps, not only because they help reduce spam on Facebook, but because every entry is a contribution back to the Archive.org project (http://www.archive.org). One of the words in the Facebook reCAPTCHA is always a word from a document scanned by Archive.org, and so your users are transcribing that text one word at a time. See http://recaptcha.net for more information on how the reCAPTCHA that Facebook uses works.
Here is example FBML code for
<fb:captcha/>
:
<form action="http://fbmlessentials.staynalive.com" method="post"> <fb:captcha showalways="true"/> <input type="submit" value="Submit Query" /> </form>
The example produces a CAPTCHA box that looks like the one in Figure 3-35.
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