How do I go about telling Captcha that my form exists? I've got a drupal situation where I want to add reCaptcha to a custom form (built in an add-on module).  You can see from the captcha admin page that there is a list of forms that I can dynamically add captcha to... but my problem is that the form I created in the add-on does not appear in this list.

I'm sure I'm missing something (perhaps in the myform_block_info function?)

Does anyone know what hook I'm looking for?  Have a working example?
This was embarrassingly easy.  See that box at the bottom of the table?  Put your form ID in there.  "myform_form"