PHP uses regular expressions to extract image links from an article, then downloads the images locally and replaces the original image links within the article.

In PHP, to extract image links from an article using regular expressions and download the images locally, you can follow these steps:

1. Retrieve the article text that needs to be processed from the web page source code.

2. Use regular expressions to match image links within text.

   preg_match_all('/<img.+?src=[\"\'](.+?)[\"\'].*?>/i', $content, $matches);
   $urls = $matches[1]; // 图片链接数组

3. Iterate through the array of image URLs and use the `file_get_contents()` function to download the images locally.

   foreach ($urls as $url) {
       $image = file_get_contents($url);
       file_put_contents($filepath, $image); // 保存图片到本地
   }

4. Replace image links in the article text with local file paths.

   $local_urls = array();
   foreach ($urls as $url) {
       $local_url = downloadImageToLocal($url, '/path/to/save');
       array_push($local_urls, $local_url);
   }
   $content = preg_replace('/<img.+?src=[\"|\'](.+?)[\"|\'].*?>/i', '<img src="' . $local_urls[$i] . '">', $content);

   The `downloadImageToLocal()` function downloads an image to the local storage and returns its local path; it should be implemented according to specific requirements.

This way, you can use regular expressions to extract image links from an article, download the images locally, and replace the image links within the article's text. Note that using regular expressions to process HTML code is a common and widely adopted approach; however, in certain special cases, other factors—such as text encoding or HTML comments—may need to be taken into account.