Change the URL for images in the sitemap if using a CDN CNAME URL on child sites running Yoast SEO.
Snippet Type
Execute on Child Sites
Snippet
function wpseo_cdn_filter( $uri ) {
return str_replace( 'http://example.com', 'http://cdn.example.com', $uri );
}
add_filter( 'wpseo_xml_sitemap_img_src', 'wpseo_cdn_filter' );