My understanding is that Blossom allows to prove ownership, like an NFT almost.
I’m a gullible person. If I watch a doctored video, does my nostr client flag it as fake? What’s the process here?
Or is this only used when someone goes to court? Or maybe that’s not how it works at all.
#asknostr
Funny you should ask. I just saw this today with Gossip client. It wouldn’t render an image because of hash mismatch. Amethyst also does something similar, showing a red ! icon if the image has been altered post-upload.
Nice! That’s exactly what I hoped it would do! That’s truly impressive.
Can you screenshot of an example when you stumble upon one of those? Very curious to see how it looks.
Here’s how it looks on Amethyst. On Gossip it’s just a highlighted text in brackets that says it won’t load image due to hash mismatch. 
Wow! Impressive.
So this is taking the note content where it already has the hash of the blossom file, comparing it with the hash of the media delivered, and detecting if they match right?
I ask because I would like to be able to explain it to others.
It wouldn’t prove ownership per se on a broader Nostr perspective, but the hash would be tied to the pubkey that uploaded it to the blossom server. So, only that blossom server or any mirrors could tie it to the pubkey. Other than Amethyst’s warning, there wouldn’t be a way to tell if any media was doctored. But, Amethyst’s feature helps in the event someone on the hosting side changed the image after it was added to the note.
Amethyst can let you know if a file has been altered from its original uploaded state.
What Blossom does is different from proving ownership. It simply proves that the contents of the referenced media has not been altered from its original form at the time it was uploaded to the Blossom server, and is therefore exactly what the author of the Nostr note intended others to see.
This is because the file name for the uploaded media is just the hash of its content. Therefore, when a Nostr client makes a request from a Blossom server for that file in order to display it to the user, it can easily check whether the hash of the content matches the file's name. If it does, the media has not been altered. If it does not match, then the client should not display the media and should show a warning, such as the red icon nostr:npub16jdfqgazrkapk0yrqm9rdxlnys7ck39c7zmdzxtxqlmmpxg04r0sd733sv mentioned previously.
Of course, this offers no proof that the video was not doctored, modified, or otherwise "fake" prior to the time it was uploaded.
So, you have no assurances that the person who uploaded the video is the "owner," or just reposting it from somewhere else, and you have no assurances that what the video shows is not fake. You only know that what the author of the note intended you to see at the time they created the note has not been altered, or else it would not have been displayed to you by your Nostr client.
First of all, thank you for the detail walkthrough! This was exactly the information I was seeking.
I might have used wrong language in my question, i think I understood the subtle differences between proof of ownership, and time of alteration happening before or after the signing of the event. But now I have a much better understanding of it.
Really appreciate your time breaking it down to me.
