在做了更多的研究之后，我找到了一种方法来做到这一点，尽管它似乎不是一个很好的解决方案，因为它需要很长的时间才能运行，因为它基本上只是在每个帖子中循环使用get_post_gallery().

也许有更好的方法，也许其他人以前也想过。

// Get All Post IDs
$post_image_query = new WP_Query( 
    array( 
        \'post_type\' => \'post\', 
        \'posts_per_page\' => -1,
        \'fields\' => \'ids\'
    ) 
);

$selected_posts = $post_image_query->posts;
$image_list_array = array();

// Loop through all posts and grab the image gallery
foreach($selected_posts as $post) {

    $post_gallery = get_post_gallery( $post, false );

    //retrieve individual ids from string
    $image_ids = explode(\',\', $post_gallery[\'ids\']);

    //build the array
    foreach($image_ids as $image_id) {
        $image_list_array[] = $image_id;
    }
}

// Get All Attachments of Posts from $post_image_query 
$the_query = new WP_Query( 
    array(
        \'post_type\' => \'attachment\',
        \'post_status\' => \'inherit\',
        \'orderby\' => \'post_parent__in\',
        \'post_parent__in\' => $image_list_array
    )
);