A prova da imagem

Pesquisador desenvolve software para detectar a autenticidade de imagens digitais e identificar a "origem" de suas partes ou "camadas' - se provenientes de uma câmera de vídeo ou foto, ou de algum programa de manipulação de imagem, como o Photoshop. Curiosa demonstração da relação paradoxal com as imagens hoje, em que crença e descrença, autenticidade e artificialidade convivem e se alimentam.

Trechos da matéria do Threat Level. Desnecessário dizer que a maior parte dos exemplos consiste em imagens de organizações terroristas.

"Using a program he wrote (and provided on the conference CD-ROM) Krawetz could print out the quantization tables in a JPEG file (that indicate how the image was compressed) and determine the last tool that created the image -- that is, the make and model of the camera if the image is original or the version of Photoshop that was used to alter and re-save the image. Comparing that data to the metadata embedded in the image he could determine if the photo was original or had been re-saved or altered. Then, using error level analysis of an image he could determine what were the last parts of an image that were added or modified. Error level analysis involves re-saving an image at a known error rate (90%, for example), then subtracting the re-saved image from the original image to see every pixel that changed and the degree to which it changed. The modified versions will indicate a different error level than the original image. You can see the difference in the two pictures (below right) of a bookshelf. Krawetz added some books and a toy dinosaur to the original image -- both of which show up clearly in the second picture after he's completed the error level analysis".