What is a Original image ?
Consider the following scenario: Alice, the copyright holder, inserts her own watermark into some object, locks the original away and keeps selling the marked image. Bob can now try to insert his own watermark into the already marked object. In case of a dispute, both Alice and Bob are able to prove the presence of “their” 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 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 after Alice and so one may conclude that Alice is the rightful owner. Unfortunately, sometimes the situation is not that simple.
Consider the following scenario: Alice, the copyright holder, inserts her own watermark into some object, locks the original away and keeps selling the marked image. Bob can now try to insert his own watermark into the already marked object. In case of a dispute, both Alice and Bob are able to prove the presence of “their” 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 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 after Alice and so one may conclude that Alice is the rightful owner. Unfortunately, sometimes the situation is not that simple.
Consider the following scenario: Alice, the copyright holder, inserts her own watermark into some object, locks the original away and keeps selling the marked image. Bob can now try to insert his own watermark into the already marked object. In case of a dispute, both Alice and Bob are able to prove the presence of “their” 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 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 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 watermark in a way that it also seems to be present in the copy Alice loc
