copymove

CopyMove, in the context of digital forensics and image analysis, refers to a form of image forgery in which a region of an image is copied and pasted within the same image. The goal is often to duplicate or conceal content, remove objects, or create misleading repetitions, making verification of authenticity more difficult.

The study of detecting such forgeries is called copy-move forgery detection (CMFD). CMFD methods are typically categorized into block-based and keypoint-based approaches. Block-based methods divide the image into overlapping blocks, extract features from each block (such as DCT coefficients, PCA components, local binary patterns, or other descriptors), and search for matching blocks to identify duplicated regions. Post-processing, including clustering, morphological operations, and selection of consistent geometric transformations, helps localize tampered areas and reduce false positives. These methods tend to be robust against simple post-processing but can be challenged by aggressive compression or significant illumination changes.

Keypoint-based methods rely on interest-point detectors (for example, SIFT, SURF, or ORB) to find matching features across the image. These approaches can be more robust to geometric transformations and some amount of post-processing, such as rotation or scaling of the copied region. They often incorporate geometric consistency checks, alignment using RANSAC, and transformation estimation to delineate duplicated areas. However, they may be less effective in tightly textured or low-contrast regions where distinctive keypoints are scarce.

CMFD is used in digital forensics, journalism verification, and forensic investigations to assess image integrity. It faces ongoing challenges from advanced edits, high compression, noise, and complex illumination, driving continual research and the development of new descriptors and fusion techniques.