How to remove header image on subpages in Twenty Eleven (default theme)?

Edit the header.php file and modify the following lines (probably around line 78-82):

Before

        <?php
            // Check to see if the header image has been removed
            $header_image = get_header_image();
            if ( ! empty( $header_image ) ) :
        ?>

After

        <?php
            // Check to see if the header image has been removed
            $header_image = get_header_image();
            if ( ! empty( $header_image ) && is_front_page() ) :
        ?>