WordPress at a glance
filter is not described

icon_dir filter-hook . WP 1.0

No thumb, no image. We'll look for a mime-related icon instead.

Usage

add_filter( 'icon_dir', 'filter_function_name_5480' );
function filter_function_name_5480( $get_template_directory()  /images ){
	// filter...

	return $get_template_directory()  /images;
}
$get_template_directory() /images
-

Where the hook is called

get_attachment_icon_src()
icon_dir
wp_get_attachment_image_src()
icon_dir
wp_mime_type_icon()
icon_dir
wp-includes/deprecated.php 1890
$icon_dir = apply_filters( 'icon_dir', get_template_directory() . '/images' );
wp-includes/media.php 830
$icon_dir = apply_filters( 'icon_dir', ABSPATH . WPINC . '/images/media' );
wp-includes/post.php 5581
$icon_dir = apply_filters( 'icon_dir', ABSPATH . WPINC . '/images/media' );

Where the hook is used (in WP core)

Does not used.