Lighting and Optical Tools for Image Forensics

1
Lighting and Optical Toolsfor Image Forensics

• Chapters 1-4

2
Introduction

• Digital Images are everywhere covers of
  magazines, in newspapers, books, and a lot of
  other places. Images can be manipulated and
  seeing is not always believing.

3
Forgery

• Forgeries have been around for years, but
• whats new about it are the tools such as
  digital cameras, computers, and software.

4
Watermarking

• One solution to image authentication problem is
  digital watermarking.
• Digital watermarking is to embed information into
  an image that can be extracted later to verify
  authencity.
• Requires specialized cameras, such as the Canon
  Eos-ID Mark II or the Nikon D2Xs

5
Forensics

• One of the most basic image manipulations is
  copy-move or cloning.
• This manipulation is necessary if a forger needs
  to cover part of an image and it can be
  successful if a homogeneous texture is available.
• Another manipulation is splicing.
• This manipulation is necessary if a forger needs
  to resize or rotate regions of an image.

6
Four New Tools

• Illuminant Direction
• If you have two people standing side-by-side, it
  is often difficult to match the lighting
  conditions from the individual photographs. The
  illuminant direction tool estimates the direction
  to the light source from several objects in an
  image widely varying estimates are evidence of
  tampering.

7
Specularity

• Human eyes are reflective and provide
  information about the lighting environment under
  which a person was photographed. The specularity
  tool estimates a 3-D direction to the light
  source from a specular highlight on the eye
  strong inconsistencies in estimates from
  different highlights across the image are
  evidence of tampering.

8
Lighting Environment

• Although the lighting of a scene can be
  arbitrarily complex, the appearance of a diffuse
  object in any scene is well represented by a
  low-dimensional model. The lighting environment
  tool estimates parameters of a low-dimensional
  model and is applicable to more complex lighting
  environments than the illuminant direction or
  specularity tools.

9
Chromatic Aberration

• Chromatic aberration results from the failure of
  an optical system to perfectly focus light of
  different wavelengths. When tampering with an
  image, this aberration is often disturbed and
  fails to be consistent across the image. Large
  inconsistencies in estimates of chromatic
  aberration from different parts of an image are
  evidence of tampering.

10
Conclusion

• The creation of digital forgery often involves
  combining objects or people from separate images.
• Four New Tools are
• Illuminant Direction
• Specularity
• Lighting Environment
• Chromatic Aberration