You have to add more than one setting. Change
$wp_customize->add_setting( 'img-upload' );
to two unique settings. i.e. img-upload-1, img-upload-2. Then call the settings in your code.
You have to add more than one setting. Change
$wp_customize->add_setting( 'img-upload' );
to two unique settings. i.e. img-upload-1, img-upload-2. Then call the settings in your code.