Enter this into functions.php

// custom background support
add_custom_background();

// The next four constants set how Twenty Eleven supports custom headers.

// The default header text color
define( 'HEADER_TEXTCOLOR', '000' );

// By leaving empty, we allow for random image rotation.
define( 'HEADER_IMAGE', '' );

// The height and width of your custom header.
// Add a filter to ftcc_header_image_width and ftcc_header_image_height to change these values.
define( 'HEADER_IMAGE_WIDTH', apply_filters( 'ftcc_header_image_width', 938 ) );
define( 'HEADER_IMAGE_HEIGHT', apply_filters( 'ftcc_header_image_height', 150 ) );

// Turn off random header image rotation by default.
add_theme_support( 'custom-header', array( 'random-default' => false ) );

// Add a way for the custom header to be styled in the admin panel that controls
// custom headers. See ftcc_admin_header_style(), below.
add_custom_image_header( 'ftcc_header_style', 'ftcc_admin_header_style', 'ftcc_admin_header_image' );

// ... and thus ends the changeable header business.

Add to Template Area

<img src="<?php header_image(); ?>" width="<?php echo HEADER_IMAGE_WIDTH; ?>" height="<?php echo HEADER_IMAGE_HEIGHT; ?>" alt="<?php bloginfo('name'); ?>" />