watermarked image

What will happen if you watermark the watermarked image?

Multiple photo watermarks can be considered as attacks in situations wherein one expects the presence of single digital watermark. Thus, any second operation of watermark embedding or any other processing on the carrier can be considered as an attack. The survival of the watermark in those cases is dependent on the application. A robust watermark is expected to survive such operations. Some watermarking tools do not allow you to insert a watermark if an image already contains a watermark from the same tool. Sometimes, a watermark from one tool may get overwritten with a watermark from another.

There are instances where, a carrier is intentionally watermarked multiple times. Consider the situation, wherein Alice buys the distrubuting rights for an watermarked image from Bob(watermark contains info about Bob). Whenever Alice sells the image to her customer, she watermarks the image with the customer information. In this situation, the final image should contain both the watermarks. The presence of both watermarks help in avoiding copyright theft and illegal copy/distrubution. In cases of multiple watermarks, the order in which different watermarks are embedded may influence the detectability. A strong watermark embedded after a weak digital watermark will mask the weak watermark and render it undetectable.