A security holes resulting from a small key space of the offset in the exiting self-embedding watermarking schemes have been pointed out.To further illustrate their insecurity

a novel forgery technique

called a 'synchronous counterfeiting (SC) attack’

is proposed and implemented on the latest self-embedding watermarking scheme proposed in the literature successfully.We also describe a possible solution to this problem of a small key space that makes our attack computationally intractable.