Automatic set a featured image from the first image's url (or tag) in the article

You can display the first image from your post content as a but can’t set that as a featured image, but you can display it.

Create a function to find the first tag from the post content starting with <img> element using regex and echo the image where you wish to display the first image. In the below function we use ob_start() which creates a buffer which output is written to.

The below code has 2 options to fetch only specific extension or only the images. Un comment the code which you are willing to use the jpg extension image and comment the other output.

<?php
function prefix_get_first_image() {
  global $post, $posts;
  $first_image="";
  ob_start();
  ob_end_clean();
  //Regex to only fetch .JPG extension images
  //$output = preg_match_all( '/<img ([^>]* )?src=[\"\']([^\"\']*\.jpe?g)[\"\']/Ui', $post->post_content, $matches );

  $output = preg_match_all( '/<img.+src=[\'"]([^\'"]+)[\'"].*>/i', $post->post_content, $matches );
  $first_img = $matches [1] [0];

  // Define the default image if no img is inserted in the content
 if ( empty( $first_image ) ) {
    $first_image = get_template_directory_uri() . '/images/default-image.jpg';
  }
  return $first_image;
}
?>

Now where you want to display the image place the following function and echo it.

<?php echo prefix_get_first_image(); ?>

I’m not a master in WordPress but yes there might be a plugin to do that but I think you might be doing this as you may have many posts with those images inserted into the content already. But its a good idea to set the featured image from media library. You should use the WordPress Native functionality rather than using custom defined methods to force the native WordPress functions.

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