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While sorting my images with

exiftool "-directory<EXIF:DateTimeOriginal" -d %Y%m%d -ext jpg .

for some of .JPGs exiftool reported an error

Warning: [minor] Error reading PreviewImage from file - ./P5030553.JPG

What does it mean, and is this something one should be worried about with regards to potential future problems and with regards to integrity of images?

Almost all images in question came from a smartphone camera and Olympus camera, with no problems during transfer or alike.

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Unless you have need of the PreviewImage, it probably isn't worth worrying about. Minor errors aren't necessarily a sign of image damage. It could be that the camera isn't writing the image metadata exactly according to the specifications or that ExifTool doesn't deal with the peculiarities of that specific camera. Given the huge range of cameras out there, both situations happen fairly frequently.

If you feel the need, you could head over to the ExifTool forums and post an example image. Phil Harvey, the creator of ExifTool, is quite likely to take a look at the image and figure out what the problem is and if need be, will quickly update ExifTool to deal with it.

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  • I keep convincing myself that must be the case, since my image collection has that error on many images that came to be through a 5 year period. It seems unlikely that they were all corrupted in the same manner, systematically on that exact tag? What is PreviewImage by the way, since the image previews and thumbnails work fine? – Rook Oct 17 '15 at 19:21
  • @Rook PreviewImage is pretty much what is sounds like. A jpg that is embedded in the image to allow programs aware of it to quickly show what the image looks like. It is usually a bigger preview than ThumbnailImage and usually part of the makernotes for the brand of camera. If you like, you can use the command ExifTool -b -PreviewImage FILE >Preview.jpg to extract the image and take a look at it. May I ask what are the cameras that this happens on? And what version of ExifTool you are using? – StarGeek Oct 17 '15 at 19:54
  • Thought as much, but how is a jpg embeeded in a jpg file (files that this happens on are all .JPGs)? The models in question were HTC Desire 300, Samsung S5, and Olympus SZ-31MR camera. exiftool -ver reports 10.00. – Rook Oct 17 '15 at 20:01
  • @Rook The JPEG format (technically JFIF) allows for a large amount of data to be in the file before the actual image. This includes, but not limited to, blocks of data such as EXIF, XMP, Photoshop data (which may include IPTC data), and ICC color profiles. Many camera models include proprietary blocks, which ExifTool collectively calls MakerNotes. These can include an embedded jpg, the PreviewImage. The Photoshop and the EXIF block can include an embedded jpeg, which is the ThumbnailImage. A simple image viewer can skip all this and go straight to rendering the image. – StarGeek Oct 17 '15 at 21:06
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    ps Is there a way to check for this error without running the above mentioned command and moving the pictures around? – Rook Oct 18 '15 at 0:41

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