We recently wanted to clean up some existing Wordpress sites for SEO, and part of that process involved fixing missing or broken IMG tags.

Here's a quick fix jquery solution for Wordpress you can use to replace IMG titles with the alt tag automatically. This way all your images without alt tags will be populated.

jQuery(document).ready(function(){
    jQuery("img").attr("title", function() {
         var theValue =  jQuery(this).attr("alt");
         return theValue;
    });
});

In action at
Printing New York
Luxury Printing
Gorilla Printing
Printing Brooklyn