Gravatar images in WordPress sites don`t have alt and title tags, with this plugin you can resolve this problem on your site.

Gravatar SEO

A light and simple plugin to insert automatically ALT & TITLE tags into Gravatar images in your site.

Jordy Meow

Rename the alternative text of your media easily directly using the Media Library, without a click.
BETA. This plugin was just created. I am waiting for the first feedbacks of my users to decide which way to go. The first thing I will implement is to update the ALT in the POSTS.
BE KIND. Again, this plugin is new. Please help us 🙂
More information available on http://apps.meow.fr/media-alt-renamer/.
<h4>Quickstart</h4>
<ol>
<li>Check the Media Library, in list view (not grid view).</li>
<li>Modify the Alt Text field, and simply type ENTER when it’s done.</li>
</ol>

Media Alt Renamer

Rename the alternative text of your media easily directly using the Media Library, without a click.

Gravatar SEO vs Media Alt Renamer