How to get customable image header?

Question

Add the below code in functions.php File of your theme. It will tells your theme to support custom headers:

$defaults = array(
    'default-image'          => '',
    'width'                  => 0,
    'height'                 => 0,
    'flex-height'            => false,
    'flex-width'             => false,
    'uploads'                => true,
    'random-default'         => false,
    'header-text'            => true,
    'default-text-color'     => '',
    'wp-head-callback'       => '',
    'admin-head-callback'    => '',
    'admin-preview-callback' => '',
);
add_theme_support( 'custom-header', $defaults );

Add this in Header.php File of your theme:

<img src="https://wordpress.stackexchange.com/questions/221224/<?php header_image(); ?>" height="<?php echo get_custom_header()->height; ?>" width="<?php echo get_custom_header()->width; ?>" alt="" />

Recommended : Custom Headers .