As making a watermark resistant to a large number of image transformation attacks is a difficult task, it is important to prioritize these transforms. A watermark should aim to be most resistant to the most common attacks; as we have pointed out, complete watermark security is an unachievable goal; it is better to target (say) 90% watermark recovery. A corollary of this is that a watermarking method must first of all be robust against those transformations used by legal users of the image. It is tempting to concentrate on the various complex attacks that malicious attackers might employ. However, this is pointless if the method is not properly resistant to image edits made by either the original owner or valid users of the image. We claim that, roughly in order of merit, a watermarking method must handle:
We will revisit this point in the next section.