pictureタグで画像のレスポンシブ

<picture>
            <source media="(min-width:769px)" srcset="<?php echo get_template_directory_uri(); ?>/assets/img/campagin1010.jpg">
            <source media="(max-width:768px)" srcset="<?php echo get_template_directory_uri(); ?>/assets/img/campagin1010-mobile.jpg">
            <img src="<?php echo get_template_directory_uri(); ?>/assets/img/campagin1010.jpg" alt="キャンペーン">
            </picture>