Image captcha does not appear on the canvas page
When I tried Drupal for Facebook I wanted to test it at your site on the canvas page.
The image captcha did not appear at all. So I could't submit my Forum topic from the canvas and went to the normal site to do it.
- Forums:

maybe fixed?
Thanks for the report. I'm not sure what was wrong.
Just today, I switched the canvas pages from FBML to iframe. Hopefully that fixed the problem. If anyone has trouble submitting from canvas pages please do let me know.
Problem with other captcha
I am using the Simple News modules on my site. When clicking on "manage newsletter subscriptions" on my fb canvas page...the captcha does not show up. I am using fbml instead of iframe. I haven't tried switching to iframe to see if that fixes it...I don't like iframe.
You could try a form alter
You could try a form alter something like this, to use facebook's captcha on canvas pages:
/**
* Implementation of hook_form_alter.
*/
function dff_custom_form_alter($form_id, &$form) {
if (fb_canvas_is_fbml()) {
// We're in a facebook callback, use Facebook's captcha
if ($form['captcha']) {
// Prevent fb_canvas from changing the form's action
fb_canvas_form_action_via_facebook($form);
// Replace captcha elements with FBML
$form['captcha'] = array('#type' => 'markup',
'#value' => '',
'#validate' => array('dff_custom_captcha_validate' => array()),
);
}
}
}
{Sorry, something is wrong with the spacing on my code filter!)