What Is EXIF Data?

EXIF in one paragraph

EXIF stands for Exchangeable Image File Format. It is a standard, first published in 1995 and maintained by the Japan Electronics and Information Technology Industries Association, for recording camera information inside an image file. Every mainstream camera and phone writes it, and virtually all photo software reads it.

How EXIF is structured

EXIF borrows TIFF's structure. It begins with a byte-order marker — 'II' for little-endian, 'MM' for big-endian — followed by a magic number and a pointer to the first image file directory, or IFD. Each IFD is a list of entries, and each entry has a tag number, a data type, a count and either a value or a pointer to one.

There are several directories, and knowing them explains a lot of otherwise confusing behaviour:

• IFD0: general image tags — Make, Model, Software, Orientation, resolution, Artist, Copyright
• The EXIF sub-IFD: capture settings — ExposureTime, FNumber, ISO, FocalLength, Flash, DateTimeOriginal
• The GPS IFD: latitude, longitude, altitude, direction and UTC timestamps
• The Interoperability IFD: a small compatibility block
• IFD1: the embedded thumbnail — a complete small JPEG copy of the image
• MakerNote: a manufacturer-specific blob inside the EXIF sub-IFD, undocumented and often large

The tags that identify you

Most EXIF tags are harmless. These are the exceptions, roughly in order of how much they give away:

• GPSLatitude and GPSLongitude — usually accurate to a few metres
• BodySerialNumber — identifies your specific camera, not just the model, and links every photo you have ever published with it
• OwnerName and Artist — a real name, typically entered once during setup and never revisited
• DateTimeOriginal with OffsetTime — when you were somewhere, and in which time zone
• Make and Model — narrows the device, and combined with other data can be surprisingly identifying
• The MakerNote block — can contain shutter counts, firmware versions and internal serial numbers

The thumbnail problem

IFD1 holds a small JPEG thumbnail, generated when the photo was taken. Some editing software updates the main image without regenerating it. The result is a file whose visible picture has been cropped or redacted, while a small copy of the original framing remains inside it.

This has caused real disclosures. It is one reason to remove EXIF from a file after editing rather than trusting the edit to have handled it.

How EXIF gets removed — and accidentally kept

Any tool that rewrites the file's container can drop EXIF. Screenshotting removes it at the cost of quality. Some resizers remove it; others faithfully carry it across. Uploading to a platform often removes it, but not always, and not for every upload path.

The reliable approach is to remove it deliberately and then inspect the result. A tool that reports what remains in the output file is telling you something; a tool that just says 'done' is not.