BountyFishing is an on-line fishing tournament where contestants submit digital photographs of their catch. Our digital forensic software is in use by BountyFishing in order to ensure that the submitted images have not been doctored.

Shown below, for example, is an original image (left), and a doctored version (right) that has been stretched to add nearly an inch to the length of the fish.

When the fish was stretched, Photoshop filled in the missing pixels by interpolating their values from the original recorded pixels. These regularly spaced new pixels are a specific combination of their surrounding pixels. Such regularities rarely occur in natural images, so their presence can be used as evidence of tampering. Shown below is the output of our software that detects these correlations -- the red-coded regions correspond to the doctored portion of the image.