app1

APP1 refers to the Application Segment 1 marker in the JPEG image file format. It is designated by the marker code 0xFFE1 and is commonly used to store metadata within a JPEG file, most notably EXIF data. The APP1 segment is optional and not all JPEGs contain it.

An APP1 segment begins with its length field, followed by its payload. If the payload starts with the ASCII string "Exif\0\0", the data is EXIF metadata encoded in the TIFF format. A TIFF header specifies endianness and an offset to the first IFD, where tags such as camera make, model, date/time, and orientation are stored.

Beyond EXIF, the APP1 payload may also carry other metadata blocks, such as XMP data, or be used by software in various ways. The primary use remains image provenance and technical data about how the image was captured. IPTC and other metadata may be stored in separate markers or streams depending on the producer.

In practice, many software tools read and preserve APP1 content when displaying or editing images, while others offer options to strip or normalize metadata for privacy or size reduction.

See also Exif, XMP, IPTC, JPEG.