Files that contain the .ithmb extension are created by Apple. These files contain a collection of "thumbnail" images, which are smaller images that link to a larger image that is located on the device that the thumbnail image is stored on. ITHMB files are used by iPod devices that can display photographic images.
The iPod photo application can display up to 25 photo thumbnails at a time. When the thumbnail is clicked on, the full version of the image can be viewed. The ITHMB files contain all of the thumbnails in a single file, with each file containing 25 different thumbnail images.
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