我不知道你是如何实现自定义格式的图像上传的。如果您遵循了标准方法，那么您应该能够使用以下任一方法获得缩略图：

get_the_post_thumbnail( $post_id, \'thumbnail\' ); get_the_post_thumbnail( $post_id, \'medium\' );

get_the_post_thumbnail( $post_id, array(300, 300))

我想知道你是否在寻找与我最初回答的不同的东西。在重读了你的帖子后，我想如果我读对了，你的图片实际上是附件，而不是缩略图。如果这些附件仍然没有保存在db中，那么只有您正确指出的关于附件的信息

在这种情况下，如果操作不当，加载附件可能会非常昂贵。令人沮丧的是，WordPress不允许您在不传递post父ID的情况下直接查询附件。

要获取帖子的附加图像，您可以尝试以下方法，这样做会更快一些

/**
 * Because we really just need post ID\'s and nothing more like
 * custom fields, postdata, and post terms, we will not be updating
 * the post cache. This saves a lot of time and resources. If you are 
 * going to need custom fields or post data or terms, then you should remove
 * cache_results because this will cause huge increase in db queries when you
 * try to get post terms or custom fields
 *
 * Also, we will only get post ID\'s as we do not need anything else
 */
$args = [
    \'fields\'        => \'ids\', // Get only post ID\'s
    \'cache_results\' => false, // Do not update post caches
    // Add any extra arguments
];
$q = get_posts( $args );

if ( $q ) {
    foreach ( $q as $id ) {
        /**
         * Get all attached images
         * 
         * We will be doing what get_attached_media does, but because we only
         * have post ID\'s and have not updated the post cache, we will not be 
         * using get_attached_media() as it will lead to a large number of db hits
         * because get_attached_media() will use get_post() to get the complete post object
         */
        $image_args = [
            \'post_parent\'    => $id,
            \'post_type\'      => \'attachment\',
            \'post_mime_type\' => \'image\',
            \'posts_per_page\' => -1,
            \'orderby\'        => \'menu_order\',
            \'order\'          => \'ASC\',
        ];
        $images = get_children( $image_args );

        if ( !$images )
            continue;

        // Loop throught the images
        foreach ( $images as $image ) {
            // Output the images as needed

            // For debugging, see the var_dump for values
            var_dump( $image );

        }
    }
}

您可以通过get_the_post_thumbnail() 作用也可以将字符串或自定义属性数组设置为第三个参数

值得注意的是，get_the_post_thumbnail() 不显示缩略图，只返回缩略图。在循环中，您可能希望使用the_post_thumbnail() 显示缩略图，在这种情况下，上述参数将分别为第一个和第二个参数。

在自定义循环中加载缩略图的成本很高，因为自定义查询不会缓存缩略图。只覆盖主查询。您需要在自定义循环中明确设置缩略图的缓存。

您可以尝试以下可能的解决方案：(NOTE: 所有内容都未经测试，可能有问题

（假设您想使用medium 调整缩略图大小，只显示缩略图，不显示其他内容，如果需要任何其他帖子属性，请删除过滤器

让我们先看看应该进入的过滤器functions.php

/**
 * Custom filter to retrieve only post ID\'s.
 *
 * We cannot set the fields arguments to ID in our query because
 * we need to update the thumbnail cache, and if you look at 
 * update_post_thumbnail_cache(), we need the post as an object
 * so we can use $post->ID, if we set the fields parameter, we only
 * get an array of ID\'s, not post objects with only ID\'s
 */
add_filter( \'posts_fields\', function ( $fields, \\WP_Query $q ) use ( &$wpdb )
{
    remove_filter( current_filter(), __FUNCTION__ );

    // Only target a query where the new wpse_fields parameter is set with a value of ID
    if ( \'ID\' === $q->get( \'wpse_fields\' ) ) {
        // Only get the post ID field to reduce server load
        $fields = "$wpdb->posts.ID";
    }

    return $fields;
}, 10, 2);

/** 
 * Because we only need to display the post thumbnails, we will not be
 * updating the term cache. If you need post term info, remove the 
 * update_post_term_cache argument. This will increase performance if you
 * do not need post term info
 */
$args = [
    \'meta_key\'               => \'_thumbnail_id\', // Only get posts with thumbnails
    \'wpse_fields\'            => \'ID\',            // Our custom argument to get only post ID\'s
    \'update_post_term_cache\' => false,           // Do not update the post caches to make the query faster
    // Any other arguments
];
$q = new WP_Query( $args );

if ( $q->have_posts() ) {

    // Update the post thumbnail cache
    update_post_thumbnail_cache( $q );

    while ( $q->have_posts() ) {
        $q->the_post();

        // Display the post thumbnail, medium size
        if ( has_post_thumbnail() ) // Not really necessary in current context
            the_post_thumbnail( \'medium\' ); // Get medium size post thumbnail

    }
    wp_reset_postdata();
}