SynthStamp only works if its server has seen what its users see: a repost can only be recognised if the original was seen first. So the add-on sends what the Reddit pages you open show, not only what you tag. Installing it and turning it on after reading its consent page is your agreement.

What the add-on sends, and why:

• The text of posts and comments on the reddit.com pages you open, their authors, their links and when they were posted — to show the tags on them, to recognise copied text, and to notice tags placed on brand-new comments.
• A fingerprint of each image and of its mirror image (256-bit PDQ hashes made in your browser), how usable the fingerprint is, the image's size and its web address — to recognise the same picture when it is reposted, resized or mirrored.
• The address of the page you are on — to know where something was seen.
• The tags you make, and when — they are the point: tags are shared counts.
• A random id, made the first time the add-on talks to the server and kept in the browser's add-on storage, which your browser may sync to your other devices — so your tags stay yours and one person counts once.
• The Reddit username you are logged in as, when the page shows it — used only to keep the counts honest, for example to spot someone vouching for their own posts; seen only by the people who run SynthStamp, never shown publicly, never treated as proof of who you are.

What it never sends: images themselves; anything from sites other than reddit.com (it does not run anywhere else); your Reddit password, cookies or votes; your email or name, which exist only if you make an account on synthstamp.com.

Your controls: one switch in the add-on's menu stops it sending page content (account tags still show, looked up by a short hash prefix). You can change or remove your own tags at any time. An account is optional. Closing your account removes your email, your name and the other personal details on it, and signs you out everywhere.

How long things are kept: tags and what was seen are kept, with no expiry for now, so nobody can tag in bad faith and then delete the evidence. When you close your account, your tags and sightings stay under an anonymous id. What the add-on sends is stored without IP addresses. If you make an account, the sign-in system keeps the IP address you registered and signed in from, for security; closing the account clears it, except from the site's own activity log. The web server keeps ordinary access logs.

Anything new the add-on collects, and every new site it runs on, will be listed on https://synthstamp.com/privacy and in the add-on before it is switched on.