  We propose a new statistic to improve the pooled version of the triangle test
used to combat the fingerprint-copy counter-forensic attack against PRNU-based
camera identification [1]. As opposed to the original version of the test, the
new statistic exploits the one-tail nature of the test, weighting differently
positive and negative deviations from the expected value of the correlation
between the image under analysis and the candidate images, i.e., those image
suspected to have been used during the attack. The experimental results confirm
the superior performance of the new test, especially when the conditions of the
test are challenging ones, that is when the number of images used for the
fingerprint-copy attack is large and the size of the image under test is small.
