gistfile1.phtml

<?php
	$sj_header_logo_default = get_template_directory_uri() . '/img/blog-logo.png';
	$sj_header_logo = get_theme_mod( 'slicejack_header_logo' );
	if ( empty( $sj_header_logo ) )
		$sj_header_logo = $sj_header_logo_default;
?>
<h1 class="title">
	<a href="<?php echo esc_url( home_url( '/' ) ); ?>">
		<img src="<?php echo $sj_header_logo; ?>" alt="<?php echo esc_attr( get_bloginfo( 'name' ) ); ?>" />
		<?php if ( is_customize_preview() ) : ?>
		<img src="<?php echo $sj_header_logo_default; ?>" alt="<?php echo esc_attr( get_bloginfo( 'name' ) ); ?>" class="default" style="display: none" />
		<?php endif; ?>
	</a>
</h1>