Depending on the way you set up your crowdsourcing form, if a person enters their Name and Email Address into the top portion of the form, it will unlock the bottom portion to be filled out and submitted. Note: If preferred, you can set up the page to only allow certain domain email addresses to unlock the page.
From the moment someone "unlocks" the crowdsourcing form, they will be listed as a "source" on your members tab within your Kapost instance. (see below) These "sources" are simply listed for your reference and do not count against your "user count." You can always track how many people are submitting ideas from outside Kapost this way.