Writing Metadata

exiftool-ts writes metadata merge-style: only the tags you pass change, every other metadata byte is preserved. This mirrors exiftool -overwrite_original semantics for license stamping and targeted edits.

Basic Write

import { ExifTool } from '@woss/exiftool';

const exiftool = new ExifTool();
const result = await exiftool.write('photo.jpg', {
  Copyright: '© 2026 Woss. All rights reserved.',
  Orientation: 1,
  Rights: 'All rights reserved. Unauthorized use prohibited.',
  WebStatement: 'https://woss.photo/license',
});

console.log(result.written); // ['EXIF:Copyright', 'EXIF:Orientation', 'XMP-dc:Rights', 'XMP-xmpRights:WebStatement']
console.log(result.skipped); // tags that could not be encoded

write overwrites the file in place and creates a <file>_original backup unless { overwriteOriginal: true } is passed.

Merge Semantics (JPEG)

Writing to a JPEG changes only the requested tags:

• EXIF tags are merged into the existing APP1 EXIF block: existing entries are patched in place or their values re-pointed; untouched entries are copied verbatim — including the ExifIFD (SerialNumber, DateTimeOriginal, LensSerialNumber, …), GPS IFD, MakerNotes (byte-for-byte), and the IFD1 thumbnail image.
• XMP properties are spliced into the first top-level rdf:Description of the existing packet without re-serializing the rest. When the file has no XMP packet, a minimal conformant one is created.
• All other segments (IPTC APP13, ICC APP2, C2PA APP11, …) are copied verbatim.
• If the file has no EXIF APP1 at all, one is created from scratch.

Key Convention

The writable keys are exported as MERGE_TAG_KEYS (MergeTagKey type):

Key	Value	Target
EXIF:Copyright	string	IFD0 Copyright (0x8298)
EXIF:Orientation	number 1-8	IFD0 Orientation (0x0112)
XMP-dc:Rights	string	XMP dc:rights (rdf:Alt/li, xml:lang="x-default")
XMP-xmpRights:WebStatement	string	XMP xmpRights:WebStatement

The group prefix is optional and matching is case-insensitive: 'Copyright' ≡ 'exif:Copyright', 'WebStatement' ≡ 'XMP-xmpRights:WebStatement'.

Any other tag from the IFD0/ExifIFD/GPS writable maps can be written with an EXIF: prefix (e.g. 'EXIF:Make', 'EXIF:DateTimeOriginal'). The entry is patched in place when it exists, appended when its home IFD exists, and reported in skipped when the file has no ExifIFD/GPS IFD.

In-Memory Writes

const outcome = await exiftool.writeBytes(imageBuffer, {
  Copyright: '© 2026',
  Rights: 'All rights reserved',
});
// outcome.bytes — new image bytes
// outcome.written / outcome.skipped

Scope Notes

• Merge writes are JPEG-only today; PNG/WebP/AVIF writers rebuild their EXIF block and do not yet support XMP splicing.
• There are no delete or clear-all semantics: an empty string overwrites the value, omitted keys are untouched.
• XMP writing beyond the two rights properties is on the roadmap (see the project scope in the README).