Digital camcorders and software programs can generate THM files, which are, essentially, thumbnail images of other media files. Typically, a THM file contains the first frame of the video file whose thumbnail it represents. The names of THM files are similar to the names of the underlying media files. For example, if a media file is called "clip001.avi," then the respective THM file can be called "clip001.thm." THM files are based on the JPEG format and can be opened by the same programs that open JPEG files.
Right click the file. Choose "Rename."
Change the extension of the file from THM to JPEG or JPG.
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Open the file.
Right-click the file if it doesn't open in Step 3. Select "Open file with" and choose Microsoft Windows Photo Viewer, Microsoft Paint, Adobe Photoshop CS5 or Apple Preview.