What is the THUMBDATA file format?
Files with the .thumbdata extension on Google Android systems are used for storing a temporary database of thumbnails for multimedia files, most importantly for images and videos stored on the device. The thumbnail database is typically saved with a filename that starts with .thumbdata followed by a version number and a device-specific hash string - common variants are .thumbdata3, .thumbdata4, and .thumbdata5 (for example .thumbdata4--1967290299).
.thumbdata system files are created on devices running Android, including smartphones, tablets, TVs, and wearables that handle multimedia content. The cache can hold thumbnails for:
- images, for example in .JPG or .PNG format,
- animations, such as .GIF files,
- videos, for example .MP4 files.
Internally the file is a proprietary binary blob: a flat index region followed by many small JPEG previews packed back-to-back, using little-endian byte order. There is no standard magic number at offset 0, but JPEG SOI markers (FF D8 FF) appear throughout at the start of each embedded thumbnail.
The database file is generated automatically to allow fast access to multimedia file thumbnails. By default .thumbdata files are hidden inside the /DCIM/.thumbnails/ folder - the leading dot hides the directory, and a sibling .nomedia file prevents the gallery app from treating the cache as a photo album. Manually deleting .thumbdata files will not damage the system; Android rebuilds the cache automatically, though thumbnail loading may be slower until it does.
On Android 10 and later, the visible .thumbdata cache has largely been superseded by per-app private thumbnail storage managed by MediaStore and Glide, so the file is now uncommon on current devices.
Security & safety
RISK: LOWThe file itself is harmless passive cache data - it cannot execute. Two real cautions: (1) Deleting it is safe and does NOT delete your photos, but only the .thumbdata cache in .thumbnails is expendable - don't delete unrelated files. (2) Privacy: because it holds previews of every photo the gallery ever indexed, the cache can contain thumbnails of pictures you already deleted; if you hand over a phone or its backup, wipe this file. 'Thumbnail recovery' is a known forensic technique - the cache can reveal deleted images.
Format details
in a nutshellPrograms that open THUMBDATA files
Windows2 apps
PhotoRec
Open-source Copy the file to a PC and let PhotoRec carve out the embedded JPEG thumbnails (low-res previews only).
HxD (hex editor)
Free Open in HxD only to confirm it's a thumbnail blob - search for repeated FF D8 FF JPEG headers. Not a real 'viewer'. 
Linux1 app
Android2 apps
Delete via Files by Google (recommended action)
Free Enable 'show hidden files', go to DCIM/.thumbnails, delete .thumbdata*; the gallery rebuilds it. There is no reason to 'open' it.
PhotoRec (JPEG carver)
Open-source Only if recovering lost previews: run a JPEG carver over the file to extract the embedded thumbnail JPEGs (low-res only). Technical details
deep spec| Format type | Proprietary binary thumbnail cache (flat index + concatenated JPEG previews) |
| Internal structure | Index/bookkeeping region followed by many small JPEG thumbnails packed back-to-back |
| Byte order | Little-endian |
| Embedded thumbnail format | Standard baseline JPEG, 24-bit color, lossy-compressed |
| Thumbnail dimensions | Small previews only (typically 512 px or smaller on the longest side); never full-resolution originals |
| Magic bytes | None at offset 0; JPEG SOI markers (FF D8 FF) appear at internal offsets where each embedded thumbnail starts |
| Version naming | Encoded in the filename suffix: .thumbdata3, .thumbdata4, .thumbdata5, plus a trailing device-specific hash (e.g. --1967290299) |
| Typical file size | Tens of MB to several GB on photo-heavy devices |
| Typical location | /DCIM/.thumbnails/ (hidden folder on Android internal storage or SD card) |
| MIME type | application/octet-stream (no registered MIME type) |
| Gallery indexing suppression | Hidden by directory dot-prefix; sibling .nomedia file stops the gallery app from scanning the cache folder as a photo album |
| Container compression | None at container level; embedded thumbnails are already JPEG-compressed |
| Safe to delete | Yes - Android rebuilds the cache automatically; deletion may temporarily slow thumbnail loading for images and videos |
| Platform | Android only (not created or read on other operating systems) |
| Cache integrity | No checksums or integrity verification; treated as expendable - Android rebuilds the file rather than repairing it |
| Superseded by | Android 10+ uses per-app private MediaStore/Glide thumbnail cache; visible .thumbdata files are rare on current devices |
| Released | Android stock Gallery / MediaStore thumbnail caching (pre-2015; .thumbdata3/4/5 across Android 4-7) |
| Latest version | No public spec; filename variants .thumbdata3, .thumbdata4, .thumbdata5 |
THUMBDATA conversions
Community Q&A
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