CCTV Still With a Twelve-Pixel Interpupillary Distance
A prosecutor sends a forensic artist a still from a convenience-store CCTV camera showing an armed robbery suspect. The image is 640 by 480 pixels, interlaced, and the suspect's face occupies about 45 by 55 pixels; the distance between the pupils is approximately 12 pixels. The suspect is turned about 30 degrees from frontal and is wearing a baseball cap that shadows the eyes. The prosecutor wants an enhanced, clear facial image for trial and asks the artist to compare it with a booking photograph of the defendant. A detective has already told the prosecutor that the defendant is the guy. The defense has not yet been notified. The artist is asked to produce a side-by-side exhibit and to state that the facial features are consistent. What should the artist do?
1. Assess whether the still is suitable for facial comparison.
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The still is not suitable for a meaningful facial comparison. A 12-pixel interpupillary distance is far below the resolution needed to assess individual facial morphology; at that scale, each pixel represents a large area of the face, and features such as the eyes, nose, and mouth are not resolved as distinct shapes. The 30-degree turn adds perspective distortion, and the cap shadow removes detail around the eyes. Interlacing may further blur the image. The artist should not treat gross similarities such as face width or skin tone as identification. The proper conclusion is that the image lacks sufficient detail for comparison, not that the defendant is consistent. The artist should document the measurements and the reasons for the limitation, and should not let the detective's prior belief influence the assessment.
2. What processing, if any, is acceptable, and what must be avoided?
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Acceptable processing is limited to operations that do not invent information: deinterlacing for display, adjusting brightness and contrast, and enlarging the image with nearest-neighbor or other transparent methods for viewing. Any enlargement must be labeled as interpolation, which adds pixels but not new detail. The artist must avoid generative fill, super-resolution tools that synthesize facial features, and selective sharpening that creates edges not present in the original. The original file should be preserved and hashed, and every processing step should be documented. If the processed image looks clearer, that clarity is an artifact of display, not evidence. The artist should explain that no enhancement can recover a 12-pixel interpupillary distance into a court-quality facial image. The booking photograph should not be used to guide the processing of the CCTV still.
3. How should the artist respond to the request for a side-by-side consistent exhibit?
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The artist should decline to state that the facial features are consistent and should explain why a side-by-side exhibit would be misleading. Placing the low-resolution still next to a booking photograph invites the jury to assume a comparison that the image cannot support, and it may amplify the detective's prior belief. If an exhibit is needed, it should show the original still with scale and resolution information, explain the 12-pixel interpupillary distance and the occlusion by the cap, and state that the image is not suitable for facial identification. The artist should not produce a demonstrative exhibit that implies a match. Any communication with the prosecutor should be documented, and the artist should be prepared to testify about the limits of the method. The defense's lack of notice is not a reason to overstate the conclusion.