human: Given a hyperedge-centered hypergraph: <hypergraph>, where the center hyperedge groups authors who co-authored the same paper.

Details of the hypergraph:
Center hyperedge (induced by source paper "Watermarking Document Images with Bounding Box Expansion"):
  Abstract: Imperceptible displacements of text objects has been shown to be a successful technique for hiding data in document images. In this paper we extend our earlier work to show how the height of a bounding box enclosing a group of text words can be used to increase the density of information hidden on a page. We present experimental results which show that bounding box expansions as small as 1/300 inch can be reliably detected, even after the distortions introduced by noisy image reproduction devices such as plain paper copiers. Digital watermarks based on this technique can be used with electronically disseminated documents for applications including copyright protection, authentication, and tagging.

Includes members:
  Member "Secure spread spectrum watermarking for multimedia":
    also connected through other hyperedges:
      - Hyperedge HE-1 (induced by source paper "Multiresolution scene-based video watermarking using perceptual models")

Question: Please tell me which research area the co-authored paper (i.e., the source paper of the center hyperedge) belongs to. The 4 classes are: Computer science, Mathematics, Engineering, Economics, Psychology, Business. Directly output the class name.

gpt: Computer science