What is the THUMBNAIL file format?
A .thumbnail file is a small preview image generated by Android to represent a larger photo or video without loading the full original. These files are stored in the hidden DCIM/.thumbnails/ directory on Android internal storage and SD cards.
In the most common case, a .thumbnail file is a standalone JPEG (beginning with the FF D8 FF SOI marker) containing a downscaled version of a photo or video frame, typically at 512×384 px or smaller. Some Android versions and gallery apps instead write a multi-thumbnail cache blob - similar to the .thumbdata family - in which multiple JPEG previews are packed into a single file without the SOI marker at offset 0.
The DCIM/.thumbnails/ directory also contains a .nomedia file, which signals Android's media scanner to exclude the folder from media library indexing.
.thumbnail files are safe to delete. Android's MediaStore and gallery applications regenerate them automatically the next time thumbnails are needed. Standalone .thumbnail files can be renamed to .jpg and opened in any image viewer.
Key facts:
- Present since early Android (pre-2.0)
- Generated by the MediaStore content provider and gallery apps such as Files by Google
- Superseded in newer Android versions by
.thumbdata4and.thumbdata5consolidated caches - Google Photos manages its own thumbnail cache separately from the
DCIM/.thumbnails/path
Security & safety
RISK: LOWPassive cache data, cannot execute. Privacy consideration: .thumbnail files are previews of every photo and video the gallery has indexed, including potentially deleted originals. When handing off a phone or sharing a backup, wipe DCIM/.thumbnails to remove these cached previews. Forensic tools use thumbnail caches to find evidence of deleted images.
Format details
in a nutshell- Windows thumbnail cache sidecar - Some Windows applications create .thumbnail sidecar files (single JPEG previews) next to media files; unrelated to Android.
- Various media applications (custom thumbnail files) - Video editors and media managers may create .thumbnail preview files; contents are typically JPEG or PNG.
Programs that open THUMBNAIL files
Windows2 apps
IrfanView
Free Open via File → Open (use 'All files' filter since .thumbnail is not a standard extension); IrfanView reads JPEG regardless of extension. 
Any image viewer (rename to .jpg)
Free Copy file to PC, rename to .jpg, open in Windows Photos, IrfanView, or any image viewer. 
Android2 apps
Any image viewer (rename to .jpg first)
Free Rename the .thumbnail file to .jpg using a file manager with 'show extensions' enabled, then open with the Photos app or any gallery.
Files by Google
Free Enable 'show hidden files' to navigate to DCIM/.thumbnails. Delete .thumbnail files to free space; do not attempt to 'open' as a gallery album. Technical details
deep spec| Primary format | JPEG - magic bytes FF D8 FF at offset 0 for standalone thumbnail files |
| Storage location | DCIM/.thumbnails/ directory on Android internal storage or SD card |
| Companion file | .nomedia file in the same directory prevents media scanner from indexing thumbnails |
| Typical dimensions | 512×384 px or smaller (photo thumbnails); video thumbnails up to 640×480 px |
| Color depth | 24-bit color (JPEG RGB) |
| Compression | JPEG lossy compression |
| Typical file size | 2 KB - 50 KB per standalone thumbnail; cache blob variants can reach MB to GB |
| Cache blob variant | May be a multi-thumbnail blob (packed JPEGs, no SOI at offset 0) depending on Android version |
| Associated OS | Android only |
| Regeneration | Deleted files are rebuilt automatically by Android MediaStore on next gallery access |
| Conversion | Standalone .thumbnail files can be renamed to .jpg and opened in any image viewer |
| Superseded by | .thumbdata4 / .thumbdata5 consolidated cache files in newer Android versions |
| EXIF metadata | Typically stripped or reduced compared to the original image |
| Released | Early Android (pre-2.0); .thumbnail extension distinct from .thumbdata* family |
THUMBNAIL conversions
Community Q&A
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