Newt Labs

This simple, lightweight plugin solves one particular issue. WordPress doesn’t include any alt text or a title tag when using Gravatars. This addresses that by using the comment author name for each of your comment’s Gravatars, and for any other Gravatar usage it should use the authors display name.
So if you create a post it will use your name for your Gravatars Alt text and Title tag and then for the comments it will use the commenters name for their Gravatars Alt text and Title tags.
With this plugin you can squash those pesky warnings given by SEO reporting tools that look for missing alt text and title tags.
<h3>Important Notes</h3>

Fix Gravatar Alt Text & Title Tag

Applies comment author name to Gravatar's Alt and Title tags in comments and author display name to Gravatars site-wide.

viljuska

WordPress plugin for auto generating image alt attribute. On image upload, if alt attribute is empty:
<ol>
<li>Generates image clean title from filename</li>
<li>Then, generates alt attribute from image title.</li>
<li>Updates image with new settings</li>
</ol>
Also, on already uploaded images, it generates alt and title if not present while image is showing on the front end.

Imager

Wordpress plugin for auto generating image alt attribute. On image upload, if alt attribute is empty: Generates image clean title from filename Then …

Fix Gravatar Alt Text & Title Tag vs Imager