WordPress at a glance
filter is not described

wp_header_image_attachment_metadata filter-hook . WP 3.9.0

Filters the header image attachment metadata.

Usage

add_filter( 'wp_header_image_attachment_metadata', 'filter_function_name_5345' );
function filter_function_name_5345( $metadata ){
	// filter...

	return $metadata;
}
$metadata(array)
Attachment metadata.

Where the hook is called

Custom_Image_Header::insert_attachment()
wp-admin/custom-header.php 1204
$metadata = apply_filters( 'wp_header_image_attachment_metadata', $metadata );

Where the hook is used (in WP core)

Does not used.