photo-metadata

# Photo metadata

## Overview

Metadata embedded in an image file travels with the file. Photo CMSs (Photo Mechanic, Lightroom, Capture One) and wire intake systems read a photo's caption, credit, and rights from its IPTC and XMP blocks, not from a separate document or the email it arrived in. If the caption, credit, alt text, and license are not *inside* the file, they are gone the moment the photo is downloaded, forwarded, or re-uploaded.

One `exiftool` pass writes the EXIF, IPTC, and XMP layers together and leaves every other tag (camera settings, shot time) untouched. Modern software reads **XMP first**, legacy IPTC-IIM second, EXIF only for date and GPS, so write XMP everywhere and add IIM as a compatibility copy on JPEG/TIFF (HEIC, AVIF, and WebP have no IIM slot at all; see `reference.md`).

Two things changed since this workflow was "caption, credit, copyright." First, **how an image was made now belongs in the metadata**: the IPTC *Digital Source Type* field labels a camera photo versus an AI-generated one, and platforms (Meta, Google) and the EU AI Act increasingly read it. Second, **cryptographic provenance (C2PA / "Content Credentials")** is arriving on wire images and cameras, a signed layer `exiftool` can *read* but not write. Both are covered below.

**A capable model already knows the field names.** The hard part is not the mechanics, it is the judgment below. Lead with that.

## When to use

- Prepping press photos for a wire so partner newsrooms can search, credit, and republish them
- Adding required photographer attribution and a reuse license before publishing or sharing
- Labeling how an image was made, a straight photo, an AI-generated illustration, an AI-edited composite
- Batch-tagging a shoot (a folder of images)
- Making images accessible (embedded alt text) and rights-clear (copyright or Creative Commons)
- Reading and sanity-checking the C2PA Content Credentials on an image that arrived from an agency

**When not to use:** editing pixels (this is metadata only); writing alt text for an HTML `<img>` (use `accessibility-compliance`); preserving web pages as evidence (use `web-archiving`); *signing* a Content Credential (exiftool can't, use `c2patool`, below).

## The discipline (what agents get wrong)

These are the failures a capable agent makes anyway. They matter more than any tag name.

1. **Caption only what is visible.** Describe what the frame shows, not what you were told. Do not infer events, intent, identities, relationships, or legal status you cannot see. "Demonstrators gather to protest a court ruling" is a claim about facts not in the frame; "A crowd holds signs outside a courthouse" is the photo.
2. **Label people from visible evidence.** Name an agency or role only from a visible marking, a labeled vest, a uniform, a badge, a patch. Otherwise write "officers in tactical gear," "a man in a blue shirt." Never assert someone's immigration or legal status (no "detainee," no "undocumented") unless it is unambiguous in the frame.
3. **Always write alt text, it is not the caption.** Write both: a short screen-reader description in `XMP-iptcCore:AltTextAccessibility` and the publishable caption in `IPTC:Caption-Abstract`. IPTC keeps these deliberately distinct, the caption states facts and is shown on the page; the alt text is read aloud by a screen reader, so do not just copy one into the other. Agents routinely write the caption and skip the alt text.
4. **Label how the image was made, and never lie about it.** If an image is AI-generated or AI-edited, say so in `XMP-iptcExt:DigitalSourceType`; if it is a straight photo, `digitalCapture` states that plainly. Do the honest thing and label it; do the diligent thing and, on an *inbound* file, **never strip an existing Digital Source Type or C2PA credential**, that erases a disclosure someone made on purpose.
5. **Strip GPS when the location could endanger someone.** A protester, a source, an abuse survivor, a minor, embedded coordinates can reveal a home or a safe house. Remove GPS from the published derivative (`-gps:all=`) while keeping the caption and credit; keep a full-GPS archival master only where location is editorial evidence. GPS is the single highest-risk tag in the file.
6. **Keep structured fields neutral.** Editorial framing or a contested label belongs in `Headline`, never in `City`, `Caption-Abstract`, or the location fields. Partner newsrooms apply their own language; clean structured fields let them.
7. **Verify the round-trip from source.** Read the metadata back *from the written file*, not from your buffer. After any upload or transfer, re-read it *from the destination*, a 200 response proves the bytes were accepted, not that the metadata survived. Most social platforms re-encode on upload and strip IPTC, XMP, GPS, *and* C2PA (see `reference.md`), so "I embedded it" is not "it arrived."

## Quick reference, the fields that carry the weight

| Role | IPTC (IIM) | XMP | EXIF |
|------|-----------|-----|------|
| Photographer | `By-line` | `dc:Creator` | `Artist` |
| Credit | `Credit` (org, max 32 chars) | `photoshop:Credit` (full name / org) | - |
| Caption | `Caption-Abstract` | `dc:Description` | `ImageDescription` |
| Alt text (short) | - | `iptcCore:AltTextAccessibility` | - |
| Extended description | - | `iptcCore:ExtDescrAccessibility` (complex images; not the caption) | - |
| How it was made | - | `iptcExt:DigitalSourceType` (full CV URI) | - |
| Keywords | `Keywords` (repeatable) | `dc:Subject` | - |
| Copyright | `CopyrightNotice` | `dc:Rights` | `Copyright` |
| License (CC) | - | `xmpRights:Marked`/`WebStatement`/`UsageTerms`, `cc:License` (legacy) | - |
| License / discovery | - | `xmpRights:WebStatement`, `plus:LicensorName`/`LicensorURL` (Google) | - |
| Headline | `Headline` | `photoshop:Headline` | - |
| Location | `Sub-location`/`City`/`Province-State`/`Country-*` | `iptcCore:Location`, `photoshop:City`/`State`/`Country` | - |
| Date | `DateCreated` | `photoshop:DateC