With the rapid growth of information technology, more and more sophisticated machines for image duplication are created to enable image reproduction in an efficient and convenient way. However, it raises a serious threat on intellectual property right. The purpose of this study is to compose digital watermarks with varied line spaces by digital halftoning in an effort to protect copyright and ensure anti-counterfeiting security. To design the line screen watermarks, we finetune varied line spaces between 1 to 6-pixel, and the Human visual system (HVS) is used to evaluate the hiding effect. Then the decrypt can be carried out by lenticular lens, copy machine and smart phone, ultimately leading to the strengthening of anti-counterfeiting mechanism of security documents. The results show that using varied line spaces screen to encrypt messages in documents can provide useful anti-counterfeiting features. The proposed method can be used to develop value-added products.