We are planning to add this, but have not gotten to it yet. Our plan was to use a javascript validation on the form field to warn users against leaving alt text empty, and to provide a reminder as to what alt text should be (concise description of important visual elements in the image).
We had originally decided against making it required (non-blank) because we felt that there are some images that should contain null alt tags (those that are only decorative or background). However, lately we are thinking that there will not likely be many such images outside of the templates. Maybe required is a better idea.
Let us know if you get anywhere on this, and the online editor issue, any time soon.
Thanks for your kind reply and help. I think it is very necessary to make the 'Alternative Image Text' mandatory input field to meet standards and validations of the page. To solve the problem regarding alt tags for decorative images, we can always use a space instead of writing anything in the "Alternative Image Text" input field when it is made mandatory.
Another thing which I have noticed is regarding the uploading of the images in an article. Anybody can upload an image in the "Related Objects" section with the use of "Upload New" button without writing any alternative image text, it totally bypasses the "Image Creation" screen. Similar thing is happening with Online editor upload functionality. So the result is anybody can upload any image without using "Alternative Image Text" straight way. We need some kind of validation there as well. What you think?
Here in the U.S. we have something called Section 508. Which means all Federal websites or websites provided under a federal contract must comply with certain accessiblity standards. One of these standards is the use of "Alt Text" tags. It would be beneficial to be able to require "Alternative Image Text" in these cases.
More info on Section 508: http://www.section508.gov
seems there is no solution up to now, to comply with w3c wai standards i made a new override-template for ezimage where i check if an "Alternative Image Text" was given for the image. if not i display the original filename as "Alt Text".