- Category: MABRC Evidence Review Board
- Published on Saturday, 02 July 2016 15:46
- Written by D.W. Lee
- Hits: 690
Photographic Analysis Protocols
1. The Board will require the person submitting the digital photographic image to provide:
….A. The Board’s Photographic Image Questionnaire must be completed and sent in with the photo image;
….B. Submitted photo must be the original, unaltered file (preferably on the original SD card) and not cropped or resized, and not resaved to another media;
….C. Photo should be created as .jpg file format;
….D. Photo size should be less than 8MB; (If applicable, if original file size is larger, arrangements will be made for delivery)
….E. Two additional comparison photos made from the same vantage point within a short period of time after the original photo was made. The first should show exactly where the subject was originally photographed showing there is nothing in place where the original photo showed the subject, and the second comparison photo showing a person or object of known size in place where the original subject was located in the original photo.
2. When the Board begins an independent analysis of the photographic image, the Board will use software applications for inspecting the metadata, searching the internet for the same or similar photo, zooming in and looking at details in the photo image, adjusting brightness or contrast, adjusting color, inverting/reversing the image from positive to negative, and analyzing Error Levels.
….A. Some of the preferred software includes uploading the image to fotoforensics.com, who provides most of the analytical tools, including access to search engines.
….B. About Metadata - Metadata is similar to documentation of the chain of custody for a digital photo. It can identify how a photo was generated, processed and last saved. Although rare, metadata can be altered (making it more difficult to detect fraud or hoax.) Although metadata does not identify exact changes made to a photo, it can help identify attributes that were changed, inconsistencies, edits and a sense of how the photo file has been managed. There is no standard for what metadata will be included in a photo. Applications can generate metadata fields, some metadata is generated during a “save”, and other fields are added to existing data. Some are updated, some retained, and some removed. This information can help an investigator to develop a timeline and identify the order of changes made to a photo. Furthermore, metadata is an invisible component of a digital photo. While not used when looking at a photo, the metadata does exist as part of the file.
….C. About Error Level Analysis – Error Level Analysis (ELA) is the identification of areas within a photo that contain different compression levels. ELA is a complicated task and requires considerable experience to draw conclusions about a photo. But when used by a knowledgeable analyst, can help determine if the photo is an original or if it has been resaved numerous times, if the photo has been rescaled, and if the image has been saved with an Adobe product, such as Photoshop (indicating possible fraud, hoax, manipulation.) ELA software applications typically display a black & white depiction of the original photo and use black and white pixels to represent various compressions. All areas within a jpeg image should normally be at the same compression level, and the image should be gray without a lot of black and white appearing in the depiction of the image. If a section of the photo has a significantly different error compression level (depicted in white pixels), it is probably a digital modification. ELA looks at the edges, textures and surfaces in a digital photo. Similar edges should have similar brightness (high contrast edges should be similar to each other, and all low-contrast edges should be similar.) In an original photo, low-contrast edges should be almost as bright as high-contrast areas in the depiction. Similar textures in the photo should have similar coloring in the ELA depiction. Similar surfaces (regardless of the actual color) should have about the same coloring in the ELA depiction. Each time an image is re-saved, JPEG looses some of the high compressions and results in less contrast in the ELA depiction.
3. Based on the analysis, the Board will formulate a response and an opinion that will be cited in the final report.