It always surprises me how often retaining attorneys send me digital copies of scanned color laser prints of photos in PDF format, or transcoded video files to do an analysis. Sometimes these images resemble their originals - sometimes they are a far cry from them.
To do the best enhancement, analysis, or authentication possible, originals are needed. Exact, logical copies of digital evidence is fine if the originals are digital.
With photographs, the original is the digital file as it came from the camera, or the negative from a film camera. If it's a PDF, it is not the original.
With security digital video recorders, the original is an exact copy of the original data recorded by the DVR. If the file plays on a standard DVD player - it probably isn't the original.
Determining if the still photos or video files are originals does involve more than simply determining whether the video plays on a standard DVD player, or if the still image file is in a JPEG file format - but those are good starts.
Whether you are using an expert or not - start demanding exact copies of the original visual evidence in your cases - it will make a significant difference in what that evidence can tell you.
George Reis, of Imaging Forensics has provided expertise to Attorneys, Law Enforcement Agencies and Insurance Companies in the areas of Forensic Photography; Photographic Authentication, Enhancement and Analysis; and Forensic Video Analysis, for over twenty years. He also provides training in these fields.
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