What is the THUMBDATA4--1967290299 file format?
.thumbdata4--1967290299 is a thumbnail cache file generated by the stock Gallery app on older Android devices, primarily those running Android 5 or 6. The app stored scaled-down previews of photos and videos in this binary file so that browsing the gallery felt faster - instead of re-reading each full-size image, it read the small cached copy directly from this file.
The file is a large binary blob that packs many JPEG thumbnail images back-to-back with an accompanying index structure. Because the container holds multiple concatenated thumbnails rather than a single image, there is no reliable magic number at byte offset 0; JPEG start-of-image markers (FF D8 FF) appear scattered throughout at the beginning of each embedded thumbnail.
The trailing number in the filename - -1967290299 in this case - is a hash or version tag computed by the gallery application. Different devices and Android versions produce different numbers, which is why you may encounter variants such as .thumbdata3--1763508120 or .thumbdata5--* on different handsets.
These files live in the DCIM/.thumbnails/ folder on internal storage or an SD card and can grow to hundreds of megabytes over time. They are safe to delete; the gallery app regenerates them on demand. Newer Android versions replaced this format with SQLite-based thumbnail databases. To recover the embedded images from an existing file, a tool such as PhotoRec can carve the internal JPEG data directly.
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 some users panic and delete the wrong thing - only the .thumbdata cache in .thumbnails is expendable. (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 a phone or its backup to someone, wipe this file. 'Thumbnail recovery' is also a known forensic technique - the cache can reveal deleted images.
Format details
in a nutshellPrograms that open THUMBDATA4--1967290299 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).
Any hex editor
Free Open in HxD only to confirm it is a thumbnail blob - search for repeated FF D8 FF JPEG headers. Not a real 'viewer'. 
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.
Any JPEG-carving / thumbnail recovery app
Open-source Only if recovering lost previews: run a JPEG carver (e.g. PhotoRec) over the file to extract the embedded thumbnail JPEGs. Technical details
deep spec| File type | Proprietary binary thumbnail cache |
| Developer | Google (Android Gallery app) |
| Primary platform | Android 5.x / 6.x (Lollipop / Marshmallow era) |
| Internal structure | Concatenated JPEG thumbnails packed back-to-back with an index |
| Embedded thumbnail format | JPEG (each thumbnail begins with SOI marker FF D8 FF) |
| Magic bytes | None at offset 0; FF D8 FF appears at each embedded thumbnail start inside the file |
| MIME type | application/octet-stream |
| Default storage path | DCIM/.thumbnails/ on internal storage or SD card |
| Filename suffix | Trailing numeric hash (e.g. -1967290299) varies by device and Android version |
| Typical file size | Tens to hundreds of megabytes on a well-used device |
| Purpose | Cache scaled-down image and video previews to speed up gallery browsing |
| Deletion safety | Safe to delete; the gallery app rebuilds the cache on next launch |
| Related versions | .thumbdata3--* (predecessor), .thumbdata5--* (successor variant) |
| Successor format | Android 10+ uses MediaStore / SQLite-based thumbnail caching |
| Thumbnail recovery | JPEG frames can be carved from the binary with tools such as PhotoRec |
| Visibility | Stored in a hidden system folder; not shown in normal file managers by default |
| Released | Android gallery thumbnail caching (pre-2015 stock Gallery); '.thumbdata4--1967290299' seen ~Android 5/6 era |
Community Q&A
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