December 18, 2007: Illusion

[Phage0070]

As I said, the shifting is very subtle and it would be difficult to see it simply by overlaying a semi-transparent image over the other. A better way is to overlay the image using the "Difference" layer quality; this method of overlay means that pixels nearly identical between the two images are made dark, while increasingly dissimilar pixels are lighter in color.

The image was compressed when it was put online, and many compression methods will leave artifacts around the edges of sharp color transitions. What would be expected from an identical image overlayed with the same compression method would be a very faint outline of sharp color transitions over an almost completely black image.

Instead we can see a sharp transition between mostly black to bright outlines, indicating the images do not match up along these transitions (where the differences are more dramatic). If the entire image was this way it would indicate the overlay was out of alignment; the fact that only sections of the image do not match suggests tampering. Once you know where to look you can see the change by alternating full opacity layers.

The first image is with the overlay matched to the bottom section. The second image has the overlay shifted down to align with the upper section. The second image shows a suggestion of another cutting about 1/3 of the way from the top, look for the horizontal bright pixels.

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