The show mentions one flaw, but it actually is not the one that I thought they found... (which, I believe are the blue lines under the NE fingers, look down about the width of the finger)
Hit the white background of the sign with a paint tool (zero threshold), if placed correctly it will fill most of the area, which is very odd. For comparison, try filling the area under the north-east finger or pull up Zoe's image, which has a similar super-white sign. Getting a proper variation in areas like that is incredibly hard, as even things like the "Add Noise" tools will not fool a careful analysis ("careful" being a touch more complex than the paint tool in MSPaint, but still not bad
).
Now look at the unfilled splotch in the top-left and compare with the one in the bottom-right. Notice that the pattern of slightly off-white pixels surrounding the blue marks are identical, which is practically impossible in a real image. Even an identical blue stamp would have slightly different lighting and error in the camera, and either would be amplified by the JPEG compression.
And now let me switch out of lecture mode and go find a movie to watch...
<edit>And I was about an inch from teasing Lindsey, who appears to have almost as much patience with this sort of thing as I do. But decided that I'd refrain from annoying moderators I hadn't had a chance to get drunk with. (That rule comes from another forum -- am not condoning underage drinking, even for those that would be legal up here).</edit>
<edit re="spelling">I swear occifer, I havn't been drunking.</edit>