Digital cameras which are manufactured nowadays tend to embed a lot of extra information in each photograph taken by the camera. This data is generally in the form of EXIF tags, and may include the make and model of the camera, the date and time the photo was taken, various camera settings for the particular shot, a thumbnail image, geolocation data (if the camera has GPS), and other details.

I only recently discovered that some cameras embed a thumbnail image within each photograph. I was even more surprised to discover that the original thumbnail may be retained, even after you have edited or cropped the image. Whether or not the thumbnail is updated depends on the image editing software that you use. Based on some testing I did, Windows Paint updates the thumbnail when the image is edited. IrfanView doesn't seem to update the thumbnail when the image is edited. Other software may or may not update the thumbnails.

If you post photographs online, you may want to consider the data embedded in your images. If you have edited your photos, do you want other people to be able to see a small version of the original image via the embedded thumbnail? If your camera has GPS, do you want other people to be able to find out the exact location of where a photograph was taken, without you explicitly telling them? Do you want people to be able to find out when a photo was taken, and with what kind of camera? You may or may not care about these details. If you do care, then you should consider stripping out the embedded data before posting the photos online.

Many popular websites appear to automatically strip out embedded data from photographs, when you upload them. This is likely done to reduce the size of the files and to reduce the amount of space required for storing the files. To determine whether a website strips EXIF data from an image, you can download the image after uploading it, and compare it to the original using software which displays the embedded data.

One program which lets you view embedded image data is WildBit Viewer. To view the embedded data, navigate and select the image file in WildBit's navigator pane, then select the menu item "File - Image Info". If the image contains an embedded thumbnail, it will be displayed in the upper right portion of the "Image Info" window. Other EXIF data will be displayed in the bottom portion of the window.

IrfanView also lets you view some of the embedded image data, if you have installed the necessary plugin. Selecting the menu item "Image - Information" will bring up a window with an "EXIF info*" button (if the image contains EXIF data). Selecting the button will display the embedded data. However, embedded thumbnails are not displayed.

IrfanView provides the option to either retain or strip out embedded image data when saving files. The "Save As" dialog for JPG files includes the following options:

  • Keep original EXIF data (if JPG to JPG)

  • Keep original IPTC data

  • Keep original JPG-comment

  • Keep original XMP data

In order to keep the embedded data, the above 4 options should be selected. In order to remove the embedded data (including any embedded thumbnail), those options should be unselected.

ExifTool is a command-line program which lets you extract, view, and/or update the metadata in image files. You can pass the program various parameters, depending on what kind of data you want to extract. For example, the command:
   "exiftool.exe -a -u -G image.jpg"
will extract and display all embedded info, including group names, from the file named "image.jpg".
The command:
   "exiftool -b -ThumbnailImage image.jpg > thumbnail.jpg"
will extract the embedded thumbnail from the file "image.jpg" and will save it as a separate file named "thumbnail.jpg".

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djinncoyote

September 2017

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