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De-identification of Facial Images by Use of Composites *Mark E. Engelstad MD, DDS, MHI Oregon Health & Science University Dept of Oral and Maxillofacial Surgery Dept Medical Informatics & Clinical Epidemiology Genevieve B. Melton, MD, MA University of Minnesota Institute for Health Informatics Department of Surgery Medbiquitous Annual Symposium, Baltimore MD May 10, 2011
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=+ Pre-op De-identification Original injury Periorbital area
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=+ Post-op De-identification
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The Questions: Do composites de-identify faces? Even those that are well-known to an observer? Are facial composites realistic in appearance?
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Figure 2: A comparison of two techniques for facial image de-identification. The middle image (B) is the original image. (A) black boxes only. (C) a facial composite, altered in the area of eyes and eyebrows only.
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This is a PRE-operative patient This is a POST-operative patient I recognize this patient
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Me Faces Subjects viewed the composite faces twice—first unaware that the faces were composites, and then primed to the presence of composites.
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Subjects viewed 20 composite faces
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10/20 had a third of a familiar face (test face) Test Face
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Results Subject ResponseUnprimed (1 st Viewing) Primed (2 nd Viewing) Facial Composites Total = 20 Composites of Unfamiliar Faces Total = 10 Did Not Identify (True Neg) 100% (120/120 ) * 42% (50/120) Identified Wrongly(False Pos) 0% (0/120)58% (70/120) Composites with Familiar (Test) Faces Total = 10 Identified Correctly (True Pos) 0% (0/120)62% (74/120) Identified Wrongly (False Pos) 0% (0/120)19% (23/120) Failed to Identify (False Neg) 100% (120/120 ) * 19% (23/120) No subjects identified test faces unless they were primed to their presence (* p < 0.001). Results
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Familiar Face Composite A Region Visible Familiar Face Composite B Region Visible Faces A and BViews by region (n) 42% (5/12) 79% * (19/24) 67% (24/36) Upper 36 71% † (17/24) 38% † 9/24 54% (26/48) MidFace 48 67% (8/12) 67% 16/24 67% (24/36) Lower 36 Total Face A 63% (30/48) Total Face B 61% (44/72) Total Faces A and B 62% (74/120) Total 120 Table 2: Identification of Test faces after priming--compared by facial region. Percentages of subjects who correctly identified a familiar face when regions of that face were visible in the composite image are shown (true positives). In Test Face B, a significant difference (* p<0.01) in identification rate existed between Upper Face and Midface. Test Face A Midface was recognized correctly more often than Test Face B Midface (†p<0.01)
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OriginalBlack BoxesComposite, Eyes only
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Making a Facial Composite 1: Photoshop 2: A Library
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Step 2,3: Remove Background, Change laterality
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4: Size all images to a standard (800 x1200) 5: Align the facial features 6: Create a Layer Mask 7: Use a Brush to reveal deeper layer 8: Blend the edges between the two layers 9: Correct Color Tones
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Show Simulation/ Example
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