The thumbs.db file is an image cache file found on Microsoft Windows operating systems. As images are accessed on the computer, the operating system builds a small information database that includes information about those images.
This database takes the form of small files, generally one per folder, and enables faster browsing in the future. Because the image information is cached in the thumbs.db files, the Windows operating system does not have to take the time to build the image information again and can simply access the existing information to display the images. The thumbs.db file can be deleted, but unless the default Windows setting is disabled, the file will be rebuilt the next time the folder is accessed.