I tumbled an issue recently that the elements don’t have an alt attribute, so I added a code that will set all empty alt with a random value.
function set_empty_img_alt_attribute( $filtered_image, $context, $attachment_id ) { $string = $filtered_image; $dom = new DOMDocument(); @$dom->loadHTML($string); $image = $dom->getElementsByTagName('img')->item(0); if($image->hasAttribute('alt')) { if( $image->getAttribute('alt') == "" ) { $image->setAttribute('alt', 'dummy alt attribute'); return($dom->saveXML($image)); } } return $filtered_image; } add_filter( 'wp_content_img_tag', 'set_empty_img_alt_attribute', 10, 3 );