What is error level analysis?

Error level analysis can establish whether a digital photograph or image has been digitally altered. Images in a jpeg file format actually lose quality each time they are resaved. The forensic analyst can take advantage of this to establish if an image has been digitally manipulated. Digital or photographic manipulation is the application of image editing techniques to photographs in order to create an illusion or deception after the original photographing took place.

Error level analysis allows the user to see the difference in quality level, represented by brightness. Things which are very bright have been edited most recently, whilst duller parts have been re-saved multiple times. This allows the user to see not just which parts of the image have been changed, but in what order the changes occurred. It should be noted that error level analysis is not reliable without further corroborating evidence. Normally we would expect to lose EXIF metadata in a processed image, either through the re-saving process or by deliberate attempts to cloak the evidence. Irregularities in the EXIF information, identifiers or compression algorithms that would normally be associated with digital manipulation should always be examined.

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