Here is the latest plugin for your wordpress blog and tit is called “ALT Images”. Plugin automatically fills the ALT attribute in HTML IMG tag on every insert a new image into the post, if it is not full.
Note 1. “AFI” does not attribute alt attribute to the images added to the media library. Note 2. On the role of ALT attribute for the search engines read here: *http://help.yandex.com/images/?id=1112581 *http://support.google.com/webmasters/bin/answer.py?hl=en&answer=114016