How to timestamp a photo
A photo already carries a date in its EXIF metadata, and that date is worth almost nothing as evidence — it comes from a camera clock anyone can set, and it can be rewritten in seconds with free tools. Here is how to get a date that actually holds up.
Why EXIF is not proof
Every camera writes a capture time into the file. It is genuinely useful for organising a library and genuinely useless for proving anything, because:
- The camera clock is set by the owner and can say anything.
- EXIF fields are trivially editable —
exiftoolrewrites them in one command. - Most platforms strip metadata on upload, so the copy online has no date at all.
- Nothing binds the EXIF date to the image content.
If a date matters — a priority dispute, an insurance claim, an evidentiary photo — EXIF alone will not carry it.
What does work
Publish a fingerprint of the image somewhere nobody can alter after the fact. The SHA-256 hash of the file is unique to those exact bytes; recording it in a public blockchain fixes a point in time that cannot be moved.
- Hash the file — computed in your browser, the photo is never uploaded.
- Record the hash on-chain — a permanent, public Ethereum transaction.
- Keep the original untouched alongside the certificate.
Verification later is a comparison: re-hash the photo, check it against the record. Match means same file, same date.
Hash the RAW, not the export
This is the part people get wrong.
Hash the RAW file (or the layered original) rather than the exported JPEG. Two reasons, both practical:
- A copier will not have it. Someone who scraped your image has a JPEG. If you can produce the RAW and a dated record proving you had it before their copy surfaced, the argument is effectively over.
- Exports are not stable. Re-exporting at a different quality setting produces different bytes and a different hash. RAW files, once written, are not touched again.
Better still, timestamp the RAW along with the frames either side of it. A copier has one image; you have the whole burst, with the same timestamp.
What it proves, and what it doesn't
The record proves that this exact image file existed by that date and has not been altered since. It does not prove you pressed the shutter — see proof of existence vs proof of authorship.
In practice that gap closes quickly. Combine the timestamp with the RAW, the adjacent frames, and the ordinary trail around a shoot, and you have evidence nobody else can assemble.
Routine that costs nothing to keep
- Timestamp on import, not when a problem appears.
- Hash the RAW, keep it read-only, work on copies.
- For a shoot that matters, timestamp the whole card at once.
- Register commercially important images with the Copyright Office as well — see how to copyright a photo.