Abstract: The use of digital photography has increased over the past few years, a trend which opens the door for new and creative ways to forge images. Now a day several software are available that are used to manipulate image so that the image is look like as original. Images are used as authenticated proof for any crime and if these image does not remain genuine than it will create a problem. Detecting these types of forgeries has become serious problem at present. To determine whether a digital image is original or doctored is a big challenge. To find the marks of tampering in a digital image is a challenging task. A copy-move image forgery is done either for hiding some image entity, or adding more minutiae resulting in forgery. In both the case, image reliability is lost. Although this technology brings many advantages but it can be used as a confusing tool for hiding facts and evidences. In this paper we detect region duplication forgery by applying Discrete Cosine Transform. We divide the image into overlapping blocks and then search for the duplicated blocks in the image.