  This letter is about a principal weakness of the published article by Li et
al. in 2014. It seems that the mentioned work has a terrible conceptual mistake
while presenting its theoretical approach. In fact, the work has tried to
design a new attack and its effective solution for a basic watermarking
algorithm by Zhu et al. published in 2013, however in practice, we show the Li
et al.'s approach is not correct to obtain the aim. For disproof of the
incorrect approach, we only apply a numerical example as the counterexample of
the Li et al.'s approach.
