Thumbs.db is a file existed and used in Windows XP, Windows Server 2003, and Mac OS X to store thumbnails cache of various graphics, pictures, photos, videos or some documents and files such as those with JPEG, BMP, GIF, TIF, PDF, AVI, MPG and HTM extension when these files are viewed in Windows Explorer’s Thumbnail or Filmstrip view. Thumbnail preview of video files are also supported in Windows XP Media Center Edition, but the previews are stored in ehThumbs.db file. Thumbs.db database files are stored in each directory where thumbnails are created.

beginning from Windows Vista, and continuing in Windows 7, Windows 8, Windows 8.1, Windows 10 or later, users will be unable to find Thumbs.db or ehThumbs.db files scatter around and place in many directories or folders again. Instead, newer Windows system stores all thumbnails and previews generated in a centralized thumbnail database. The centralized thumbnail database is located in the following folder:

\Users\[User Account Name]\AppData\Local\Microsoft\Windows\Explorer
The centralized thumbnail database applies to local folders only. Thumbs.db continues to apply to network folders or shared folders only.

Inside the above folder, there are a few files with prefix thumbcache with filename has the format similar to thumbcache_xxxx.db. So you can no longer delete thumbs.db. To remove the thumbnail cache, simply use Disk Cleanup.