Location of image metadata on my server

Question

To clean up my media library, I deleted some unused pictures directly out of my uploads folder. Now, whenever I go to the media library the file names are still there but the thumbnails have been deleted: https://snag.gy/lzCLiF.jpg

Where is the image metadata stored on my server so that I can delete it there.

Answer 1

The image url is store in wp_posts as an attachment post_type with their corresponding posts(s) as parents. From Codex, see Template Tags Show All Attachments

I believe something like this would retrieve all attachments in DB outside of a loop:

   global $post;
   $args = array( 
         'post_type' => 'attachment', 
         'posts_per_page' => -1, 
         'post_status' => 'any', 
         'post_parent' => null 
          ); 
   $attachments = get_posts( $args );
  if ( $attachments ) {
    foreach ( $attachments as $post ) {
        setup_postdata( $post );
        the_title();
        the_attachment_link( $post->ID, false );
        the_excerpt();
    }
    wp_reset_postdata();

Perhaps something like this could find and clear those no longer available in /uploads/ directory:

$args = array(
      'post_type' => 'attachment',
      'numberposts' => -1
      );
$attachments = get_posts( $args );
foreach( $attachments as $attch ){
    $file = get_attached_file( $attch->ID );
    if( !file_exists( $file ) ){
        wp_delete_post( $attch->ID, false );
    }
}

Reference for get_attached_file()

Reference for wp_delete_post()

Look into those those and it should be rather straightforward how to achieve the cleanup you need.