Section 8.3. Document Forgery

8.3. Document Forgery

One advantage of using PDF files for document transfer is that they can be digitally signed and even encrypted. Signatures are overkill for most applications, but in the case of an especially sensitive document, they offer an important safeguard, preventing a malicious third party from changing the document after it has been released. This technology has been around for a number of years, but it's not as widely used as it could be. I predict this will change over time as more cases emerge where electronic documents have been modified or forged in order to commit fraud or to embarrass, discredit, or blackmail people.

Two dramatic examples of forgery came to light during the 2004 U.S. presidential election. The fact that sophisticated forgeries were created with the sole intent of influencing public opinion is very disturbing and does not bode well for future election campaigns.

CBS News aired a story in September 2004 concerning President Bush's service in the Texas Air National Guard in 1972. The report was based on documents that turned out to be forgeries. Even though the materials they were given were in the form of physical pieces of paper that appeared to date from that era, their electronic origin was revealed by careful analysis of the scanned documents. What gave them away was the presence of superscripts in several places. For example:

Bush wasn't here during rating period and I don't have any feedback from 187^th in Alabama.

Electric typewriters in the seventies could not produce superscripts that were scaled down in size like the th in 187^th. That suggested that a word processor had been used. Typing the same text in Microsoft Word, scaling the text to fit the scanned memo, and overlaying the two produced a remarkable concordance.

The original story, with links to the scanned memos and to the later internal review by CBS, is available at http://www.cbsnews.com/stories/2004/09/08/60II/main641984.shtml. An extremely detailed analysis of the typography in the memos, written by Joseph Newcomer, can be found at http://www.flounder.com/bush2.htm.

The second example involved a photograph of John Kerry appearing to share the stage at an anti-Vietnam war rally in 1970 with the actress Jane Fonda (see http://www.snopes.com/photos/politics/kerry2.asp). The photograph was published on the conservative web site NewsMax.com in February 2004. It caused quite a stir, especially among veterans, as it suggested a more radical side to Kerry's character than had been presented thus far. The picture was quickly revealed as a fake by Ken Light, the photographer who took the original picture of Fonda at a rally in 1971, one year after the supposed joint appearance. The fake image was a clever composite. The image of Fonda had been carefully excised from its image and then placed next to Kerry. Her image appears in front of the background trees but behind the papers that Kerry is holding in his hand. With hindsight, you can tell that the light on their faces is coming from two different directions, but overall it's a pretty good fake.

The selective manipulation of digital photographs is nothing new. Pick up any of the tabloid papers in a U.S. supermarket and you're bound to see an example on the cover. But the tremendous recent growth in digital photography, and the ease with which images can be retrieved from the Web, are destined to make abuses of the art ever more frequent. Digital signatures and watermarks offer a way to protect future images, but there is little we can do to guard against the manipulation of historical material.