How to fix millions of Alt Text are missing on body content?
Try using the Search and Replace Scanner module to search through the text of your body field. You could use a regular expression to search for image tags without alt attributes.

Some excerpts from the module page:


  Features
  
  
  Can search and replace text in CCK text fields, in addition to standard node title and body fields
  Plain text search and replace regular expression search and replace
  Case sensitive search option
  


This module is designed to work on MySQL and dedicated servers, be sure to review the module page and accompanying documentation.