captcha not showing in jot

Hi, I tried to turn on captcha for a comments page but the captcha doesn’t appear. Can’t figure it out. Appears on the user login page ok. Tried jot call cached and uncached (!) but nothing works - just doesn’t show. Any ideas anyone?

The call is:

[[Jot? &pagination=`4` &badwords=`{{badwords}}` &captcha=`1` &canmoderate=`Site Admins` &moderated=`1` &notifyAuthor=`1` ]]

[+search+] [+permission+] [+summary+] [+jotCall+]

thanks

David Heriot