wp_customize_image_control default value

I am trying to create a custom theme using WordPress 3.4’s customization options. I would like to create an option to change the theme’s logo, but I would like to also display a default logo image.

I am using the following code in my function.php page:

$defaultbranding = "get_bloginfo('template_directory') . '/images/logo.png";

    $wp_customize->add_setting( 'change_branding', array(
        'default' => get_bloginfo('template_directory') . '/images/logo.png',
    ) );

    $wp_customize->add_control( new WP_Customize_Image_Control( $wp_customize, 'change_branding', array(
        'label'   => 'Image Control',
        'section' => 'theme_settings',
        'settings'   => 'change_branding',
    ) ) );

And in the theme’s header.php page:

src='<?php echo get_theme_mod( 'change_branding' , 'default' ) ?>'

I would like the ‘default’ value on the front end to be:

get_bloginfo('template_directory') . '/images/logo.png'

Is there some way I can achieve this?

Thanks in advance for any help.