How to tell if a photo has been manipulated? Math.

Ann Dooms (Photo: TEDxBrussels/Scorpix)

Ann Dooms (Photo: TEDxBrussels/Scorpix)

Ann Dooms is a mathematician who specializes in forensics of a very specific kind — multimedia. The Vrije University researcher uses clever math to analyze digital media — photos and videos — and suss out foul play. “We play our daily episode of ‘CSI: Multimedia,’” she explains in a talk at TEDxBrussels sharing the ways she and her team at the university work on forensics projects.

How does multimedia forensics work? From her talk:

This is a photo of a cat.



Zoom in.



No, really.



Here is what those pixels look like when encoded by color:



These numbers offer Dooms a grand opportunity … for math.


Algorithms can be used to find “patterns, irregularities, additions, and changes,” she says, like …


in these two photos …


which may look the same, but … the numbers say otherwise.


The photos in numbers.



 The inconsistencies in those numbers …


reflecting changes that Dooms made to the colors in the photos “barely noticeable to the naked eye” that allow Dooms to do things like hide an entire cat in a scattered image:




Watch her whole talk to learn more:

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