I would like to add the media description as a data-attribute to each image of the gallery. All the other answers favour the solution to copy the whole code from media.php to functions.php and change it there. But isn't there a more intelligent way?
It's way to much code duplication in order to change one single line of code!
If anybody is interested: I managed it to add a data attribute to the article thumbnail with following filter:
function post_thumbnail_add_data_attribute( $input, $post_image_id ) {
$caption = wptexturize(get_post(get_post_thumbnail_id())->post_excerpt);
$substitute = is_home() ? "<img" : "<img data-description=\"" . $caption . "\"";
return str_replace("<img", $substitute, $input);
}
add_filter('post_thumbnail_html', 'post_thumbnail_add_data_attribute', 10, 3 );
For the gallery I followed the advice to remove the gallery shortcode...
remove_shortcode('gallery');
and then to add a customized gallery function to the functions.php...
add_shortcode('gallery', 'my_gallery');
which contains the tiny customization...
// Add the caption of images in a gallery as the name attribute in order to fetch it with jQuery lightbox
$output = str_replace('<img', '<img data-description="' . wptexturize($attachment->post_excerpt) . '"', $output);