carestad

If your site is depending on posts to have their thumbnail images set, this is the plugin for you. Also makes it possible 
to require tags in every new post.
When trying to save a post without at thumbnail or tags and when activated, the user will get a warning and the post will 
be saved as a draft instead.

Post Requirements

This plugin allows you to require posts to have thumbnail set and/or tags.

shawfactor

I wrote this plugin as I needed full flexibility when adding an “agree to terms” check box to your login or registration forms,
Not only does this plugin facilitate requiring users to agree, but also allows you to customise and configure the terms and conditions message, add links, and also the customise the message those who have not agreed see.
Additional features include:
<ul>
<li>User registration support</li>
<li>Buddypress support</li>
<li>Multisite support</li>
</ul>

LH Agree to Terms

Add a HTML5 "Agree to terms" check box on login or registration forms.

Post Requirements vs LH Agree to Terms