What is the THUMBDATA4--1763508120 file format?
.thumbdata4--1763508120 is a proprietary binary cache file created by Android's stock Gallery application on mid-2010s devices, particularly associated with the Android 5 and 6 era. It belongs to the .thumbdata family of hidden thumbnail-index files stored on the device's internal storage or SD card, typically inside the DCIM/.thumbnails/ folder.
The file is not a single image. Internally it consists of a bookkeeping index region followed by many small JPEG thumbnails packed back-to-back - one preview per photo or video ever processed by the gallery. There is no documented magic number at byte offset 0; JPEG SOI markers (FF D8 FF) appear scattered throughout at the start of each embedded thumbnail, not at the container's own header.
The trailing number in the filename - here --1763508120 - is a signed-integer hash generated by the gallery app on that specific device and Android build. It is not a user-chosen name and varies between devices, which is why you may also see variants such as .thumbdata3 or .thumbdata5 on other handsets.
Because the cache grows continuously (one entry per indexed image), it can reach several gigabytes on heavily used devices. It is entirely safe to delete; Android will recreate it the next time the gallery scans your media. On newer Android versions and Google Photos, thumbnail caching migrated to app-internal storage, so these visible .thumbdata4 files are rarely seen on modern handsets.
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--1763508120 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| Format type | Proprietary binary thumbnail cache - concatenated JPEG thumbnails with an internal index |
| MIME type | application/octet-stream |
| Encoding | Binary; each embedded thumbnail is a standard JPEG stream |
| Container structure | Internal bookkeeping/index region followed by JPEG thumbnails stored sequentially, one per indexed image |
| Compression | JPEG per individual thumbnail; the outer container adds no extra compression layer |
| Magic bytes | No stable magic number at offset 0; JPEG SOI markers (FF D8 FF) appear at the start of each internal thumbnail, scattered throughout the file |
| Typical file size | Tens of MB to several GB; grows continuously as new images are indexed |
| Color depth | 24-bit color per embedded JPEG thumbnail |
| Thumbnail dimensions | Small preview sizes only - typically tens to a few hundred pixels per side; never full-resolution originals |
| Default storage path | DCIM/.thumbnails/ on device internal storage or SD card |
| Associated platform | Android (prominent in Android 5 and 6 era stock Gallery app) |
| Filename hash suffix | The trailing signed integer (e.g. --1763508120) is a per-device/per-build hash; it differs across handsets and Android versions |
| Format generation | Part of the .thumbdata family: .thumbdata3 (older), .thumbdata4 (mid-era), .thumbdata5 (later variant) |
| Superseded by | App-internal thumbnail caching in Android 8+ and Google Photos; .thumbdata4 files rarely appear on modern devices |
| Cache behavior | Safe to delete; the Android gallery or MediaStore rebuilds the cache automatically on the next media scan |
| Released | Android gallery thumbnail caching (pre-2015 stock Gallery); '.thumbdata4--…' seen ~Android 5/6 era |
Community Q&A
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