Often end users have unrealistic expectations of the strength of the watermarking process - they expect it to be infallible. In fact, with sufficiently small images it is impossible to guarantee that a watermark will be retained. As we have pointed out, to some extent these problems can be overcome by good user-interface design. However, watermarks should still be seen as aid to efficiently tracking copyright violations, rather than as a secure means of asserting copyright.
A real-world watermarking system should be robust in the face of image transformations, but must handle particularly common transformations (scaling and compression) best of all. The system must also be clear in its design goals: using a single watermark scheme for multiple purposes will lead to security compromises. Unfortunately the currently available commercial watermark systems fall some way short of these goals.