DateSealed: A Free Way to Record When You Published Something, Without Uploading It

日本語版: 「いつ公開したか」を第三者の台帳に残す無料ツール DateSealed を公開しました

I am a photographer, and I run an SEO business. Both jobs share one nasty moment: you find your photo or your article on someone else’s site, and the question comes back at you: “Can you show you published it first?”

Often the honest answer is “sort of”. The CMS says a date, but the CMS date can be edited. The file’s metadata can be edited. A screenshot can be edited. What you want is a record that someone other than you wrote down, at a time you cannot rewrite afterwards.

So I built DateSealed: a free tool that records when a text, a photo or a web page existed, and keeps that record somewhere I cannot change either.

Why I did not use something that already exists

This started with the property photos of a real-estate company I run. I wanted to protect them from being altered or lifted by other sites, so I first looked at what already exists in Japan. This is what I found, as of November 2026.

Notarial fixed date (確定日付). A notary stamps a date on a paper document for 700 yen. There is an electronic version for the same fee, but it accepts only text, PDF and XML files up to 10 MB, goes through the Ministry of Justice’s online filing system on weekdays, and you contact the notary office first. Good for a contract; not for a steady stream of photos and articles.
Copyright registration (Agency for Cultural Affairs). Registering the first publication date costs 3,000 yen per work and gives a legal presumption of that date. It is a paper application, one per work, after publication.
Accredited time stamps (certified by the Minister of Internal Affairs and Communications). Priced for companies: for example 120,000 yen a month for 1,000 stamps at one provider, or 8,800 yen a month for 1,000 at another. One reseller offers an email-based service with five free stamps a month and 40 yen per stamp after that, aimed at companies.
Blockchain services. The Japanese ones I found are for businesses: a Toyota service for corporate records, and a Tech Bureau archiving service from 500 yen a month. An overseas browser extension, ProofSnap, captures web pages and hashes files with Bitcoin anchoring, from about 5 dollars for ten captures, with no free plan.
In-camera signing (C2PA). Sony, Nikon and Canon now sign photos at capture on some models. That answers where a file came from, which is a different question from when it was published, and the two go well together.

All of these are useful, and I say so on DateSealed’s own pages. What I could not find was the combination I wanted: free, no account, the hash made in the browser so nothing is uploaded, a record anchored somewhere the operator cannot change, and a WordPress plugin so it happens on every publish. So I built it.

How it works

Your browser hashes the data. A SHA-256 hash is a 64-character fingerprint of a file or a text. It is computed inside your browser. Your photo or article is not uploaded.
You get a signed time stamp immediately. DateSealed returns a standard RFC 3161 time stamp signed by its own time-stamping authority.
The hash is also anchored in Bitcoin. It is sent to public OpenTimestamps calendar servers, and within hours it is written into a Bitcoin block. From then on, anyone can check the date against the Bitcoin ledger alone, even if DateSealed disappears.

That second layer is the point. A time stamp I sign is only as trustworthy as I am. A Bitcoin block is not mine to change.

What it does not do

I want to be precise here, because the wrong expectation is how people get hurt.

A record shows that data matching this hash existed at that time. It does not show that the content is true, that you made it, or that you hold the rights.
It does not guarantee legal effect. In Japan, the time stamps that carry an official status are those from providers accredited by the Minister of Internal Affairs and Communications. If you need one of those, use an accredited provider.
Think of DateSealed as one more piece of evidence, cheap and quick to make, to put next to the rest of your evidence. That is all.

Four ways to use it

Paste a text or pick a file on the home page. The hash is made in your browser.
Enter a page URL. The server fetches the public page once and records two hashes: one of the page’s main text (menus, footers and ads excluded) and one of the raw HTML. It keeps only the hashes and the URL, never the content. The record page also lists the dates the page claims about itself, clearly marked as unverified.
Use the WordPress plugin. On every publish and update, it hashes your post on your own server and sends only the hash. Each revision gets its own record, so your first publication is never overwritten. It needs PHP 8.2 or newer.
Call the API. POST /api/v1/proofs with {"sha256": "..."} is all it takes. Documentation is at datesealed.com/api.

Check it without trusting me

Every record page lets you download the .tsr (the signed time stamp) and the .ots (the Bitcoin proof), plus the certificate. You can verify them on your own machine:

openssl ts -verify -digest <sha256> -sha256 -in <id>.tsr -CAfile ca.pem
ots verify <id>.ots

The root certificate’s SHA-256 fingerprint is 64:D0:D6:F2:89:BE:13:FC:98:D7:73:27:FE:D7:80:47:E0:C3:0D:09:F6:36:41:83:0E:7D:21:D7:CA:B9:82:2B. The root key was generated on my own computer and is encrypted with a passphrase that only I know; it was never on the server. The server holds only the time-stamping key.

Privacy and limits

Hashes, record times and the proof files are stored. If you use URL input, the URL you entered is stored too, and never shown on public pages. IP addresses are kept only as salted hashes for 30 days.
No cookies.
The limits are 10 records an hour and 50 a day per IP address. URL input counts as two records. Pages are fetched up to 2 MB, and pages that draw their text with JavaScript give only the raw-bytes hash.
It is available in 20 languages, with English as the default. The translations are machine-assisted, so if you find a wrong sentence, tell me.

Try it

Open datesealed.com, paste a sentence and press the button. It takes a few seconds, and nothing is uploaded.

DateSealed is operated by Lightscend Co., Ltd. I would like to hear where it breaks and what you would want it to do next, especially from photographers and bloggers who have been through a “who was first?” argument.