Exposing Photo Manipulation
with Inconsistent Reflections
James F. O’Brien
University of California,
Berkeley
Hany Farid
Dartmouth College
Presented by: Jinjie Lin
All images presented in this document is from the paper except the ones whose source link are provided.
Where can we get the lastet SIG papers?
http://kesen.realtimerendering.com/
Photographs can no longer be trusted!
Is this a real photo?
A forged image
Is this a real photo?
http://img2.zol.com.cn/product/22/406/ceIi7JPRpyOnI.jpg
Is it really so easy?
Is this a real photo?
Digital watermarking
• Embedding information
into a digital signal which
may be used to verify its
authenticity or the
identity of its owners
• Drawback
– Watermark must be
inserted at the time of
recording
Passive forensic techniques
• Operate in the absence of watermarks or
signatures.
• Assumption:
– Although photo manipulation may leave no
obvious visual clues, it may alter some geometric
or statistical property in the image.
Exposing Photo Manipulation with
Inconsistent Reflections
Planar reflection geometry
reflection
object
Surface normal
viewer
Reflecting mirror
Planar reflection geometry:
The reflection Vanishing Point
Observation:
- PR must be perpendicular to MB
- Photo: liner perspective projection
- Parallel lines must all converge to
the same vanishing point.
Planar reflection geometry:
Reflection Line Midpoints
Observation:
The reflection line midpoint must lie
in the plane of the reflecting surface.
Planar reflection geometry:
Reflection Line Midpoints
p
r
Test:
- for a line pr, check whether it converge to the same vanishing point v;
- Compute the midpoint, m;
- Compare m to other scene elements for consistency.
Planar reflection geometry:
The Center of Projection
http://cs.hust.edu.cn/webroot/courses/csgraphics
/jiaocai.php?bookpage=7_d
http://www.cse.unr.edu/~bebis/CS791E/Notes/PerspectiveProjection.pdf
Observation:
For a given image, the center of projection is unique.
How to find out the center of
projection from an image
• When vanishing points for three mutually
orthogonal directions are known.
Common in man-made environments
How to find out the center of
projection from images
• The computation is extremely unstable.
• Instead, they compute a cloud of plausible
locations rather than a single location.
Detecting Inconsistencies
• Three tests for exposing inconsistencies in an
image
– ill-defined reflection vanishing points
– Implausible midpoints
– Inconsistent centers of projection
• Not all of these tests are applicable to any
given image.
– Require some human understanding of the image
content.
Results
lack of a well-defined reflection vanishing point
each object has a well-defined reflection vanishing point,
but they are mutually inconsistent.
Blue lines: scene features with their corresponding reflections in the building windows.
Green: linear features that should be perpendicular to the building front
head has been removed
the height of her hair has been altered.
Conclusion
• Present a set of test to expose photo
manipulation.
• Require the input photo should contain planar
reflectors where parts of the scene can be
observed both directly and indirectly through
reflection.
• Is not able to prove a photo is authentic, but it
can prove a photo is fake.