What is original image

What is original image brfore watermarking?

Consider the following scenario: Alice, the copyright holder, inserts her own photo watermark into some object, locks the original away and keeps selling the marked image. Bob can now try to insert his own image watermark into the already marked object. In case of a dispute, both Alice and Bob are able to prove the presence of watermark and claim ownership of the document. How can this situation be resolved?

The "traditional" answer is: look at the objects, Alice and Bob claim to be the original. Alice's original should not contain a photo watermark, whereas Bob's "original" must contain Alice's watermark (if we assume that Bob cannot remove marks). This situation would indicate that Bob inserted his watermark software after Alice and so one may conclude that Alice is the rightful owner.

Unfortunately, sometimes the situation is not that simple. It has been shown that, in particular class of watermarking schemes, Bob can insert his digital watermark in a way that it also seems to be present in the copy Alice locked away (although he has no access to it). So Alice's original contains Bob's mark and Bob's "original" contains Alice's mark. This type of attack is called "inversion attack" or more "dead lock attack". There is no way to resolve copyright ownership in this case. This result indicates that watermarking images "alone", that is without a carefully designed protocol around it, will not suffice to resolve the copyright situation.