diff --git a/core/includes/theme.inc b/core/includes/theme.inc
index 2b06429..caee49d 100644
--- a/core/includes/theme.inc
+++ b/core/includes/theme.inc
@@ -1266,16 +1266,10 @@ function template_preprocess_links(&$variables) {
  *     full URL.
  *   - width: The width of the image (if known).
  *   - height: The height of the image (if known).
- *   - alt: The alternative text for text-based browsers. HTML 4 and XHTML 1.0
- *     always require an alt attribute. The HTML 5 draft allows the alt
- *     attribute to be omitted in some cases. Therefore, this variable defaults
- *     to an empty string, but can be set to NULL for the attribute to be
- *     omitted. Usually, neither omission nor an empty string satisfies
- *     accessibility requirements, so it is strongly encouraged for code
- *     calling _theme('image') to pass a meaningful value for this variable.
- *     - http://www.w3.org/TR/REC-html40/struct/objects.html#h-13.8
- *     - http://www.w3.org/TR/xhtml1/dtds.html
- *     - http://dev.w3.org/html5/spec/Overview.html#alt
+ *   - alt: The alternative text for the image to make its visual information
+ *     accessible to people browsing with an assistive device or in text-only.
+ *     An alt attribute must be included for images that convey information:
+ *     http://www.w3.org/html/wg/drafts/html/master/embedded-content.html#alt
  *   - title: The title text is displayed when the image is hovered in some
  *     popular browsers.
  *   - attributes: Associative array of attributes to be placed in the img tag.
@@ -2540,19 +2534,7 @@ function drupal_common_theme() {
       'template' => 'dropbutton-wrapper',
     ),
     'image' => array(
-      // HTML 4 and XHTML 1.0 always require an alt attribute. The HTML 5 draft
-      // allows the alt attribute to be omitted in some cases. Therefore,
-      // default the alt attribute to an empty string, but allow code calling
-      // _theme('image') to pass explicit NULL for it to be omitted. Usually,
-      // neither omission nor an empty string satisfies accessibility
-      // requirements, so it is strongly encouraged for code calling
-      // _theme('image') to pass a meaningful value for the alt variable.
-      // - http://www.w3.org/TR/REC-html40/struct/objects.html#h-13.8
-      // - http://www.w3.org/TR/xhtml1/dtds.html
-      // - http://dev.w3.org/html5/spec/Overview.html#alt
-      // The title attribute is optional in all cases, so it is omitted by
-      // default.
-      'variables' => array('uri' => NULL, 'width' => NULL, 'height' => NULL, 'alt' => '', 'title' => NULL, 'attributes' => array()),
+      'variables' => array('uri' => NULL, 'width' => NULL, 'height' => NULL, 'alt' => NULL, 'title' => NULL, 'attributes' => array()),
       'template' => 'image',
     ),
     'breadcrumb' => array(