Access: [1.1.1.1]: <img> missing 'alt' text
  Priority 1

Cause:

All images -- including transparent gifs -- must have "alt" text. Alternate text should be concise (i.e. 10-12 words maximum). For transparent images and spacers, use alt="" (NULL), alt=" " (spaces are acceptable), or alt="blank". Any words depicted in the image should also appear in the "alt" text description.

Testfile:


<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" "http://www.w3.org/TR/REC-html40/loose.dtd">
<html lang="en">
<head>
<title>aert1.0/1.1.1</title>
</head>
<body>
<img src="noAlt.jpg">
</body>
</html>


References:

W3C WAI: http://www.w3.org/WAI//

HTML Techniques for WAI 1.0: http://www.w3.org/TR/WCAG10-HTML-TECHS/