[trip42]

You mean YouTube has information on all of the photographs I've ever taken and who I've licensed them to? I don't recall making this information public, so I don't see how they could possibly detect copyright infringement of my content.

[CGamesPlay]

The copyright infringement detection technology is opt-in. You disclose to YouTube the licensees.

[noduerme]

Throw one of your images at tineye.com. It's a reverse image analysis tool; their algorithm is under wraps, but I'm sure a few people around here could speculate on how it works. It works nicely with cropped and scaled images, which is a hint =)

[Natsu]

Infringement depends on permission. No third party can possibly know whether or not the use of a given work was authorized or not unless told by the copyright holder.

Now, when told by the copyright holder that no use of some work is authorized, they can flag all copies of it that they are able to find and match it under the assumption that nothing is authorized. But you couldn't add anything if we assume that every user is lying about being authorized.

Moreover, as was demonstrated in the Viacom case, even the copyright holders get it wrong. In particular, Viacom had uploaded copies of their own works and made them appear leaked. Yet these were uploaded by Viacom itself and, thereby, authorized. They even had to go back and have them put up after taking them down by mistake. And they had to remove them from their complaint after being told of their mistakes. Twice. After doing due diligence with expensive lawyers.

[sv123]

I think his point was that you can certainly detect an image in use on other sites but that does not matter because it may or may not be infringement. Nobody could possibly know if he licensed his work to be used by certain sites or not.

[noduerme]

The comment you guys are responding to was in jest. I wrote the original post in this subthread. My point about Tineye was that it's obviously capable of picking up duplicates (which is the immediate question I was responding to) and equally incapable of determining which of those duplicates are licensed.