When I moved my house to nguyenvanquan7826.com, I had a problem in importing data, all photos i uploaded missing. I can’t spend all day to download and set featured image for all articles. Fortunately, almost images in the articles I uploaded to imgur.com and post it later, so they are still there.I tried to find way to get these images in article to set it as thumbnail image and I found two ways.
set featured by image in article

Option 1: Use the code

First, you copy the below function into function.php file:

function get_first_image() {
  global $post, $posts;
  $first_img = '';
  $output = preg_match_all('/<img.+src=[\'"]([^\'"]+)[\'"].*>/i', $post->post_content, $matches);
  $first_img = $matches[1][0];
  if(empty($first_img)) {
    $first_img = "/path/to/default.png";
  return $first_img;

Then open index.php file (or content.php) and find the function which calls old images, most of them use function the_post_thumbnail(). With me, it is:

<?php if ( has_post_thumbnail() ) { ?>
    <?php echo '<div class="featured-thumbnail">'; the_post_thumbnail('featured',array('title' => '')); echo '</div>'; ?>
<?php } ?>

Replace it by:

<img src="<?php echo get_first_image(); ?>" alt="<?php the_title(); ?>" />

It will effects on home page, you can set on tag, search or category into archive.php file, category.php file, tag.php file.

Option 2: Use plugin

You can use plugin External URL To Post Thumbnail. However, i haven’t ever used that way so if you use, please tell me about it!

Đọc bản tiếng Việt tại dây!