Files with .THUMBDATA extension are used by Google Android to store a temporary database of thumbnails for images and movies. The Thumbnail Database is saved with an extension starting with .THUMBDATA and containing unique identifiers like hyphens, numbers or strings.
THUMBDATA files are not meant to be opened. To solve issues with THUMBDATA files, associate the extension with an app on your device. On Windows, right click a THUMBDATA file, choose “Open with” and select an app. Check “Always use this app” box. On Mac, right click the file, click “Open with” > “Other…” and select an app. Check “Always Open With” box.
If no app supports THUMBDATA files, download and install one that does. The system will then associate that app with THUMBDATA files automatically. If it fails to associate, manually associate the file extension with the app as described above. Android apps may support THUMBDATA files.
To prevent Gallery app from recreating THUMBDATA files you deleted, give the new file the same name. Note Gallery may load thumbnails slower without its THUMBDATA files. What is a THUMBDATA file extension? It is created by Google for Android thumbnail databases. THUMBDATA files store temporary data.
Android OS
Photo Recovery Tools