What is the THM file format?
.thm is a format used for storing small raster images (thumbnails) that depict equivalent full-size images or video frames in a reduced scale.
.thm files are most commonly generated by digital cameras and camcorders - including models from Canon, GoPro, Sony, Olympus, and Panasonic - as compact preview images paired with their recorded video clips. Each .thm thumbnail typically accompanies a video file (such as an MP4 or MOV) under the same base name, giving media managers and operating systems a quick visual reference without loading the full clip.
Despite the distinct extension, a .thm file is internally a standard JPEG image - it begins with the familiar FF D8 FF JPEG signature and carries the image/jpeg MIME type. Typical resolutions are small, such as 160×120 pixels, which is intentional: the compact size means thumbnails load and render quickly in galleries and file browsers, saving screen space while still giving a meaningful preview. Because the underlying data is plain JPEG, opening a .thm file is as simple as renaming it with a .jpg extension - any image viewer will open it immediately.
.thm files are also produced by some photo-editing and video applications, and they may appear alongside CR2 or other camera RAW photo files as sidecar preview images.
Security & safety
RISK: LOWA camera .thm is an ordinary JPEG preview - low risk, the same as any image file (the only theoretical concern is a malformed image targeting a viewer bug, so keep your viewer updated). It contains no executable code. You can delete .thm (and GoPro .lrv) files freely; they're just previews and don't affect the real video. The only caution: a file claiming to be '.thm' from an untrusted source could be something else renamed - check it's actually a JPEG (FF D8 FF) before trusting it.
Format details
in a nutshell- Sony Ericsson phone theme - An obsolete theme package for 2000s Sony Ericsson feature phones, not an image.
- Application thumbnail database - A thumbnail-cache/database file used by some older clip-art galleries and apps, not a JPEG.
Programs that open THM files
Windows3 apps
IrfanView
Free Open the .thm directly (IrfanView reads it as JPEG) or use it to batch-rename/convert .thm to .jpg. 
Microsoft Photos
Built-in Rename the file to .jpg and double-click - it opens as a normal image. (Or set Photos to open .thm.) 
XnView MP
Free Open and view the .thm thumbnail; good for browsing/batch-converting many camera files. 
macOS1 app
Preview
Built-in Rename to .jpg and double-click, or open from Preview; macOS shows it as a JPEG image. 
Android1 app
Google Photos / any gallery app
Free Rename the file to .jpg, then open it in your gallery/Photos app to view the thumbnail. Technical details
deep spec| File structure | Plain JPEG data with a renamed extension; internally identical to a standard .jpg file |
| MIME type | image/jpeg |
| Magic bytes | FF D8 FF at offset 0 (JPEG Start Of Image marker) |
| Typical resolution | 160×120 px (common on Canon DSLRs and GoPro cameras); exact resolution varies by device |
| Color depth | 24-bit RGB (standard JPEG color encoding) |
| Compression | Lossy DCT compression, same algorithm as standard JPEG |
| Typical file size | Usually under 10 KB due to low resolution and JPEG compression |
| Paired file | Accompanies a video or RAW file sharing the same base name (e.g. GOPR0001.thm + GOPR0001.mp4) |
| Camera manufacturers | Canon, GoPro, Sony, Olympus, Panasonic, and other DSLR and camcorder makers |
| Sidecar role | Lightweight preview sidecar; lets cameras and media software display a still frame without decoding the full video |
| Aspect ratio | Matches parent media - typically 4:3 for stills, 16:9 for widescreen video |
| Color space | sRGB (default JPEG color space used by virtually all camera makers) |
| EXIF metadata | May embed EXIF data including GPS coordinates, camera model, and capture timestamp |
| Extension rename | Renaming .thm to .jpg is sufficient to open the file in any image viewer or editor without conversion |
| Released | Long-standing convention on DSLRs and camcorders; widely seen on GoPro since the 2010s |
| Open standard | Yes · royalty-free |
| Specification | www.loc.gov |
THM conversions
Community Q&A
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