What is EXIF metadata?

The short answer

EXIF — Exchangeable Image File Format — is the standard cameras use to record information about a photograph inside the photograph. It sits alongside the compressed image rather than inside it, which is why removing it changes nothing you can see.

It was designed in the 1990s so that photographers could review their settings after a shoot. The GPS part came later, and it is the part that most often surprises people.

What is actually in there

EXIF is structured as a TIFF directory with three parts, and knowing which is which helps when you are reading a metadata report:

• IFD0 — the basics: Make, Model, Orientation, Software, Artist, Copyright, and the file modification date.
• The Exif sub-directory — the photographic detail: ExposureTime, FNumber, ISO, FocalLength, LensModel, Flash, and DateTimeOriginal, often with sub-second precision.
• The GPS sub-directory — latitude, longitude, altitude, a UTC timestamp, and sometimes the direction the camera was pointing.

The MakerNote

Most cameras also write a MakerNote: a proprietary, undocumented blob that can run to tens of kilobytes. Manufacturers use it for things the standard does not cover, and its contents vary by model and firmware.

Because it is undocumented, no tool can reliably tell you everything inside one. What is known is that it can contain a body serial number and a shutter actuation count — which makes it one of the more identifying parts of a photo, and a good reason to remove metadata rather than edit it field by field.

Where EXIF lives in a file

In a JPEG, EXIF sits in an APP1 marker segment near the start of the file, before the compressed scan data. In a PNG it lives in an eXIf chunk. In WebP it is a RIFF chunk named EXIF. In HEIC it is an item in the file’s item store, located through a table called iloc.

In every case it is separate from the pixels. That separation is what makes stripping it lossless: the compressed image data is copied across byte for byte and never decoded.

What EXIF cannot tell you

EXIF is written by software and can be changed by software. It is a record of what a device claimed, not proof of what happened. Any field in any file can be edited by anyone with the right tool — including this one.

That matters in both directions: it is why you can correct a wrong timestamp, and why a timestamp should never be treated as evidence on its own.

Questions