PRNU Suppression
Definition
Any processing that reduces the usable PRNU signal in an image: heavy JPEG compression, resolution downscaling, in-camera noise reduction, social-media re-encoding, and post-processing filters. Suppression reduces PCE for true matches and raises the risk of false negatives.
- Common causes
- JPEG compression, downscaling, in-camera noise reduction
- Also caused by
- Social-media re-encoding, post-processing filters
- Effect on PCE
- Reduces peak-to-correlation-energy for true matches
- Risk
- Increased false negatives
Common questions
Why does uploading a photo to social media risk defeating a later PRNU comparison?+
Most platforms re-encode uploaded images at reduced resolution and quality to save bandwidth, which strips away much of the fine per-pixel noise the PRNU method relies on, so an image pulled back down from that platform may fail to match its true source camera even though it genuinely came from it.
How does an examiner account for PRNU suppression when reporting a non-match result?+
A responsible report distinguishes a genuine non-match from an inconclusive one caused by known suppression sources in the image's processing history, since a low correlation score after heavy compression or resizing does not reliably rule the camera out.
Related terms
- Anti-Forensic PRNU Suppression
- Deliberate actions to remove or obscure the PRNU fingerprint, such as adding PRNU-erasing noise, applying heavy lossy compression, or scaling and re-cropping...
- Base Rate Problem
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- Individual vs Device-Class Attribution
- Individual attribution identifies one specific camera body. Device-class attribution identifies only the make or model. PRNU provides individual attribution; metadata and lens-distortion...
- Shared Device Model
- The scenario in which multiple individuals use the same camera. The PRNU fingerprint links an image to the device, not to any...
- Uncertainty Quantification in PRNU
- Expressing a PRNU attribution result not just as a binary yes/no but with stated PCE values, false-positive rate at the threshold used,...