Focusing on the instability of concealment and display that occurs when embedding a latent image via a phase modulation technique, a scheme was proposed to obtain good anti-counterfeiting quality by adjusting latent image boundary dots. Weber law was used to analyze the dot arrangement characteristics of a latent image area and the corresponding hidden layer. Results indicate that the inner dots of the latent image did not affect the concealment, whereas the boundary dots had a great impact on its overall concealment. The boundary adjustment method was deduced based on the boundary dot location distribution; thus, the displacement, compensation position, and area adjustment coefficient were determined. Results show that the improved method outperformed the conventional phase modulation method under the premise of ensuring ensuring extracting effect, and provide a new optimization scheme for the grating anti-counterfeiting technology.