A THUMBDATA3-1967290299 file is a data file created by the Gallery app included with select Android phones, such as HTC Desire SV and Sony Xperia. It contains indexed properties about every thumbnail image stored in the Gallery app to help it load thumbnail images quicker.

The THUMBDATA3-1967290299 file is created by the Gallery app to cache information about images that have been indexed. The caching helps the Gallery app load images quicker and reduce lag time when displaying thumbnails. The more images you have in the Gallery app, the larger the THUMBDATA3-1967290299 file grows. It may become several hundred MBs, or in some cases, several GBs in size if you have a large number of thumbnail images in your Gallery app. The file increases in size every time a new image is added and even when an image is deleted the indexed properties of the image still remain. You can use an Android file manager to navigate to your thumbnail index files, which can be found in the sdcard/DCIM/.thumbnails directory. To reduce the THUMBDATA3-1967290299 file size, you need to remove images from the Gallery app then delete the THUMBDATA3-1967290299 file. The file will be regenerated by the Gallery app but only for the images stored in the app. NOTE: The THUMBDATA3-1967290299 file is commonly found with the .THUMBDATA3-1763508120 file.