settings->callbacks->media_upload( array(
'option_name' => 'wpo_wcpdf_settings_general',
'setting_name' => 'wcpdf_settings[wpo_wcpdf_settings_general][header_logo]',
'id' => 'header_logo',
'uploader_title' => __( 'Select or upload your invoice header/logo', 'woocommerce-pdf-invoices-packing-slips' ),
'uploader_button_text' => __( 'Set image', 'woocommerce-pdf-invoices-packing-slips' ),
'remove_button_text' => __( 'Remove image', 'woocommerce-pdf-invoices-packing-slips' ),
) );
?>