Forensic camera identification Flashcards
What does the Protection of Children Act 1978 act state?
It restricts the making of child pornography or what looks like child pornography
What is illegal to do under the Counter-Terrorism Act 2008?
It is an offence under the Counter-Terrorism Act 2008 to publish or communicate a photograph of a constable a member of the armed forces, or a member of the security services, which is of a kind likely to be useful to a person committing or preparing an act of terrorism.
What is it an offence to do under section 58 of the Terrorism Act 2000?
It is an offence under section 58 of the Terrorism Act 2000 to take a photograph of a kind likely to be useful to a person committing or preparing an act of terrorism, or possessing such a photograph.
What is it a criminal offence to do when a person is in court?
It is a criminal offence (contempt) to take a photograph in any court of any person, being a judge of the court or a juror or a witness in or a party to any proceedings before the court, whether civil or criminal, or to publish such a photograph.
What is shot noise due to?
Shot Noise: This is due, in part, to the random fluctuations in photon energy captured by the image sensor. These variations are recorded in the image as visible noise.
What causes readout noise?
Readout Noise: Is electrical charge built up within the camera from the different onboard processes, which leaves random noise within the image.
Why aren’t short noise and readout noise good for camera identification?
For shot and readout noise, the positions of the noisy pixels differ from image to image
- Both shot noise and readout noise are random additive noises.
What are the two types of fixed noise patterns?
- Photo Response Non-uniformity (PRNU)
- Dark signal non-uniformity (DSNU)
Why does dark signal non-uniformity noise occur?
Fixed pattern noise due to ‘dark currents’ that occur in the sensor even when no light is incident upon it. Easy to remove with dark frame subtraction.
Why does photo response non-uniformity noise occur?
Is the variation in pixel sensitivity caused by manufacturing defects and the natural non-uniformity of the silicon used in the image sensor.
Why is fixed pattern noise helpful?
Fixed pattern noise still has the speckled pattern but the aspect of the speckled pattern doesn’t change from image, it’s always in the same location from image to image. This creates a unique ‘fingerprint’ for cameras.
Why is DSNU not as helpful?
DSNU can be removed with frame subtraction, high-end cameras can do this automatically. Therefore this is not useful in photo forensics.
Why is photo response pattern noise helpful?
Pattern noise is consistent and unique to the sensor and therefore the camera and can be used to relate an evidential image to a camera. You can have a camera with the same make and model however the PRNU will be different.
How can you obtain a ‘fingerprint’ for a specific camera?
- Take at least 50 natural scene images using a suspected source camera.
- Individually filter each image using a wavelet denoising filter.
- Average together the filtered images to produce a unique fingerprint for the camera.
What is a wavelet denoising filter?
- SImilar to a smoothing or averaging filter
- The wavelet filter is better as its more sensitive and removes noise more efficiently
- The filter is not 100% efficient it can remove other details in the image.
