In reply to Ivica Delic.

Fortunately, there's an even simpler way to add alternative text to your images. Manually add the appropriate text to the alternative text field when adding the image to your post. Humans will always be the best at determining the contents of an image, as well as determining how to describe that image's contents. Despite all of this, I'm glad this plugin exists. Appropriate alternative text for images requiring it is probably the lowest hanging fruit when it comes to accessibility, and alternative text is probably the most neglected part of making a website accessible. I should go propose this as a feature project.