选择数组元素或删除前两个

我正在改编一个生成缩略图的WordPress插件。多亏了这个网站，我已经进步了，但我被困在一个问题上。该插件从帖子中的第一个图像生成缩略图。我需要从第三张图像生成的。

帖子内容

[URL=http://example.com/viewer.php?file=3030128910131424.jpg]      [IMG]http://example.com/images/30301289149131424_thumb.jpg[/IMG][/URL] [URL=http://example.com/viewer.php?file=6331951274718152.jpg][IMG]http://example.com/images/7633127470118152_thumb.jpg[/IMG][/URL]

原始代码

// Initialize variable used to store list of matched images as per provided regular expression
$matches = array(); 
// Get all images from post's body
preg_match_all('/'[img']([^'[']>]*)/i', $post[0]->post_content, $matches); 
if (count($matches)) {
    foreach ($matches[0] as $key => $image) {
        /**
         * If the image is from wordpress's own media gallery, then it appends the thumbmail id to a css class.
         * Look for this id in the IMG tag.
         */
        preg_match('/wp-image-(['d]*)/i', $image, $thumb_id);
        $thumb_id = $thumb_id[1];
        // If thumb id is not found, try to look for the image in DB. Thanks to "Erwin Vrolijk" for providing this code.
        if (!$thumb_id) {
            $image = substr($image, strpos($image, '"')+1);
            $result = $wpdb->get_results("SELECT ID FROM {$wpdb->posts} WHERE guid = '".$image."'");
            $thumb_id = $result[0]->ID;
        }
        // Ok. Still no id found. Some other way used to insert the image in post. Now we must fetch the image from URL and do the needful.
        if (!$thumb_id) {
            $thumb_id = apt_generate_post_thumb($matches, $key, $post[0]->post_content, $post_id);
        }
        // If we succeed in generating thumg, let's update post meta
        if ($thumb_id) {
            update_post_meta( $post_id, '_thumbnail_id', $thumb_id );
            break;
        }
    }
}
}// end apt_publish_post()
 /**
  * Function to fetch the image from URL and generate the required thumbnails
 */
 function apt_generate_post_thumb($matches, $key, $post_content, $post_id)
 { 
 // Make sure to assign correct title to the image. Extract it from img tag
$imageTitle = '';
preg_match_all('/<'s*img [^'>]*title's*='s*['""'']?([^'""''>]*)/i', $post_content, $matchesTitle);
if (count($matchesTitle) && isset($matchesTitle[1])) {
    $imageTitle = $matchesTitle[1][$key];
}
// Get the URL now for further processing
$imageUrl = $matches[1][$key];
$imageUrl = str_replace("_thumb", "", $imageUrl);

我尝试了两件事

// Get the URL now for further processing
$imageUrl = $matches[3][$key];
$imageUrl = str_replace("_thumb", "", $imageUrl);

不生成缩略图。

现在我正在尝试在获取 url 之前删除前两个数组变量。我已经尝试了array_splice和array_slice但我没有得到任何结果。从第三张图像而不是第一张图像创建缩略图的任何想法？谢谢！