My brand new WordPress plugin Header Image Description grabs header images description hardcoded in functions.php (or in other places) and serve it for ALT, TITLE or other usage in template files.
Primary supports Twenty Ten and Twenty Eleven themes, but can be used in all themes that follow styling with header image.
Based on my self answered question on WP support forum Get header image description to string.
How to use?
First provide description in hardcoded image set in functions.php, something like this:
'footonsand' => array( 'url' => '%s/images/headers/sand_and_foot.jpg', 'thumbnail_url' => '%s/images/headers/sand_and_foot-thumbnail.jpg', 'description' => __( 'Sand and Foot by Aleksandar Urošević', 'twentyten' ) ),
After installing and enabling HID from Plugins admin page, open your header.php template file, find line
<img src="<?php header_image(); ?>" width="<?php echo HEADER_IMAGE_WIDTH; ?>" height="<?php echo HEADER_IMAGE_HEIGHT; ?>" alt="" />
alt="<?php header_image_desc(); ?>"
If you wish to display header image description in image tooltip, also add TITLE tag similar to ALT tag:
title="<?php header_image_desc(); ?>"
Download from WordPress