At the time I wrote this article, there had been a couple of online articles about faked (or Photoshopped) photographs, especially ones used by reputable news organizations. I decided to take a look and do some research about how it was possible to detect faked photographs, especially those that are not really obviously done. The obvious fakes are, well, obvious, and funny, to boot.
Pretty quickly I was led to the research of Professor Hany Farid, who seems to be the expert on image forensics. His various papers are quite fascinating to read, although I warn you some are behind paywalls.
When I mentioned the topic to my editor Alex Cox before writing the article, he came up with the brilliant idea of sending me a couple of images he’d taken, Photoshopped with the intent of seeing whether I could find out what had been altered in each. I used an online tool called Error Level Analysis (sadly no longer active. although FotoForensics seems to have taken on the mantle) written by Dr Neal Krawetz to test the provided images, as well as an image I’d taken so that I had a baseline. I’d have to say the results weren’t that obvious and more than a little ambiguous. (For the score: I’d spotted all the alterations to the Stourhead photo, but missed one in the Pulteney Bridge image. Can you find what I missed?)
(For convenience, here are the links to images mentioned in the article:
I will also note that just recently there was another kerfuffle over a faked photo from a war zone, this time in Syria.)
This article first appeared in issue 307, May 2011.
You can read the PDF here.
(I write a monthly column for PCPlus, a computer news-views-n-reviews magazine in the UK (actually there are thirteen issues a year — there's an Xmas issue as well — so it's a bit more than monthly). The column is called Theory Workshop and appears in the Make It section of the magazine. When I signed up, my editor and the magazine were gracious enough to allow me to reprint the articles here after say a year or so.)