I'm developing a forum/community board and I want to avoid registration forms. So I decided to make user registration almost implicit.

What I mean is, if an unregistered user is about to do something that requires an account (*e.g.* creating a thread, responding to one, sending a PM to someone else, etc.), just add an `email` field and a `CAPTCHA` in whatever the form is.

Then, when the form with the `email` field and the `CAPTCHA` is submitted, along with the main information of the form (the `thread text`, `response text`, `message content`, respectively), the user's account is automatically created. The section `My account` become available, etc. And the an email is sent to the email they provided along with a randomized password (their current password).

But I have a few questions about this approach:

* What if the user makes a mistake when writing his/her email?
* Is it okay to add a time limit for validating the account (like 24 hours
or so)? And should the account be deleted completely if this time limit is exceeded?

And most importantly, how can I make it clear for users that this is only for registration, and if they already have an account they should just sign in?