Glossary
Embedded thumbnail
An embedded thumbnail is a small copy of an image stored inside its own metadata block, for fast previewing.
Updated
Cameras write a small preview into the EXIF block so that file browsers can show a thumbnail without decoding the full image. It is an ordinary compressed image, just a very small one.
The interesting property is that it is generated at capture and not always regenerated afterwards. An image cropped or redacted by software that updates the pixels but not the thumbnail can ship a preview still showing the original frame — including whatever was cropped out. This has produced real disclosures.
Because the thumbnail lives inside the EXIF block, removing EXIF removes the thumbnail with it.
Related terms
- EXIF — EXIF is the metadata standard cameras use to record how, when and where a photo was taken, stored inside the image file itself.
- Maker note — The maker note is a proprietary, largely undocumented section of an EXIF block in which a camera manufacturer records whatever it likes.
- Lossless — Lossless means the image data comes out bit-for-bit identical to what went in.