Simple Captcha: Session ID as identifier?

[eluser]erik.brannstrom[/eluser]
Hi!

I built a captcha library which randomly generates a simple mathematical question that the user is required to answer correctly to submit the form. When the user loads the controller, a new captcha is generated and the answer is stored in a database table along with the session ID which is the identifier used to fetch the correct answer once the user has pressed submit.

So my question is, is the session ID a smart way to associate a user with an answer, seeing as (if I understand it correctly) the session ID is changed every five minutes or so?

Best regards,
Erik Brännström