Добавить одинаковые описания на все фото gallery wordpress

Добавить плагин – The Gallery Image Captions (GIC)

Затем добавить код. в function

// This will display a default caption for attachments with empty captions.
function my_default_gallery_image_caption($attachment_id, $captiontag, $selector, $itemtag) {

    $id = $attachment_id;

    $my_image_meta = galimgcaps_get_image_meta($id);

    $caption_string = ( !empty( $my_image_meta['caption'] ) ) ? $my_image_meta['caption'] : 'YOUR CUSTOM CAPTION GOES HERE';

     return "<{$captiontag} class='wp-caption-text gallery-caption' id='{$selector}-{$id}'>" . $caption_string . "</{$captiontag}></{$itemtag}>";
}
add_filter('galimgcaps_gallery_image_caption', 'my_default_gallery_image_caption', 10, 4);