WordPress at a glance
filter is not described

get_header_image_tag filter-hook . WP 4.4.0

Filters the markup of header images.

Usage

add_filter( 'get_header_image_tag', 'filter_function_name_3373', 10, 3 );
function filter_function_name_3373( $html, $header, $attr ){
	// filter...

	return $html;
}
$html(string)
The HTML image tag markup being filtered.
$header(object)
The custom header object returned by 'get_custom_header()'.
$attr(array)
Array of the attributes for the image tag.

Where the hook is called

get_header_image_tag()
wp-includes/theme.php 1082
return apply_filters( 'get_header_image_tag', $html, $header, $attr );

Where the hook is used (in WP core)

Does not used.