Pre-Printing image is referred to as digital print proof validated by copy-editor. This type of image is stored in binary screened form after being processed by raster image processor (RIP). It has indubitable legitimacy once the digital print proof is finalized. Looking at the overall printing flow, however, pre-printing images are still at the risk of malicious tampering in the storage and transmission process. Most of existing copy-move forgery detection methods employing high dimensional feature vector have high computational complexity, thus are not applicable to color separated binary screened proofs. In this paper, a new approach for copy-move forgery detection is proposed based on digital halftoning technology. The original image is binarized via digital halftoning technique in CMYK color space, which is similar to raster image processor. Then the halftone image is tiled to overlapping blocks, and the local screen density features of halftone overlapping blocks in CMYK channels are extracted for copy-move forgery detection. Experimental results demonstrate that the proposed method is able to detect copy-move forgery regions precisely, and it is robust to rotation and small scale zooming attacks to forgery regions.