The following table is adapted from CreativeCommons.org:

Name	Characteristics
Version 3.0 Licenses:
Attribution
CC By. Usage requires citing, referencing of the creator/source. For OERs this is the most “open” license, in my opinion. Unlike Share Alike (see below), it does not mandate any particular license on subsequent adaptations or derivations.
Attribution-NoDerivs
CC By-ND. Usage additionally mandates that no derivative works or adaptations may be made. For OERs I think this is most applicable when a creator is concerned about losing the integrity of the original work if adaptaions, derivations, or remixes are made.
Attribution-NonCommercial-NoDerivs
CC By-NC-ND. Usage additionally mandates that no commercial use will be made of the work, whatever that means. This is for paranoid creators of OERs, or those who legitimately want to protect the integrity of their work..
Attribution-NonCommercial
CC By-NC. See above. I think this is an underused license in OERs, as it stipulates non-commercial usage but doesn’t limit adaptations to using the same license.
Attribution-NonCommercial-ShareAlike
CC By-NC-SA. Usage additionally requires that any derivatives, remixes, or adaptation of the work be licensed under the same Creative Commons license. This seems to be the most common CC license for OERs, as it stipulates that all uses are non-commercial, presumably “for educational purposes only”, and preserves the open-ness of the work and any and all future derivatives.
Attribution-ShareAlike
CC By-SA. See above. This is a common CC license for OER where the creator wants to forever preserve the open-ness of the work and all derivatives.

Additionally, there are two notable licenses in draft on the Creative Commons wiki:

Creative Commons Zero (CC0)

According to Creative Commons, Creative Commons Zero (or CC0)…

…is a protocol that enables people to WAIVE to the fullest extent possible under applicable copyright law all rights they have and associate with a work so it has no (or minimal) copyright or neighboring rights restrictions attached to it.

In the US we typically call such works “public domain”, but some writers (e.g. Terry Hancock in FreeSoftware Magazine) have noted that public domain is not a license at all, while CC0 will be.

Creative Commons Plus (CC+)

Creative Commons Plus (or, CC+) is simply an existing Creative Commons license plus “some other agreement which provides more permissions” or, perhaps, requirements. For example, Creative Commons refers to a commercial license “tailored for specific uses with specific names of copyright holders”.

Commentary: I like the idea of both of these additional licenses, as Creative Commons has made the idea of sharing works more accessible and understandable, but is not yet sufficiently encompassing for all uses. Plus and Zero seem to fill the gaps, and for open education might provide creators and institutions with flexibility while still conforming to the Creative Commons label in such a way that basic usage is more instantly understandable (without reading through paragraphs of legalese).

Set Up Blog Post Licenses

1. From within any blog post, add a new Custom Field called, for instance, “license”.

2. Use an easy, consistent tactic for marking your license. I’m using lowercase letters separated by dashes to describe Creative Commons licenses, e.g. cc-by-sa or cc-by-nc-nd. Use these marks in each post’s “license” field from now on.

Now you’re storing the license metadata on your blog’s server. It’s time to make it look cool in your theme.

Customize Your WP Theme

1. Isolate your theme’s folder in wp-content/themes

2. Upload whatever CC license images that you want to use to your theme’s images folder. Here’s a ZIP file of the CC images I use. Note how I named the images the same way I entered my licenses above, e.g. cc-by-sa.png or cc-by-nc-nd.png. This allows me to shortcut in the PHP.

3. Now the “hard” part: edit the files single.php and (optional) index.php. Find the spot you want to have your license display. This needs to be soon after the WP function the_content() is called. In index.php this needs to happen before the endwhile of the have_posts() function.

4. Write (or paste in) a little PHP. In short we need to use the get_post_meta() function to get the custom field value for this post. Here’s a quick snippet that I used to test theis approach:

   <?php
   if($license = get_post_meta($post->ID, "license", "true")) {
?>
   <a href="http://creativecommons.org/licenses/"><img src="<?php bloginfo('template_directory'); ?>/images/licenses/<?=$license?>.png" alt="<?=$license?> license" style="border: 0" /></a>
<?php
   } else {
   ?>
   &copy; <?php the_time('Y');
   }
?>


   If there is nothing in the “license” custom field, it defaults to © and the post’s year.

   You can do this on both single.php and index.php or anywhere else you have post information showing.

5. Finally, upload and test!