The sensor pattern noise (SPN) is a unique attribute of the content of images that can facilitate identification of source digital imaging devices. Owing to its potential in forensic applications, it has drawn much attention in the digital forensic community. Although much work has been done on the applications of the SPN, investigations into its characteristics have been largely overlooked in the literature. In this study, the authors aim to fill this gap by providing insight into the characteristic dependency of the SPN quality on its location in images. They have observed that the SPN components at the image periphery are not reliable for the task of source camera identification, and tend to cause higher false-positive rates. Empirical evidence is presented in this work. The authors suspect that this location-dependent SPN quality degradation has strong connection with the so-called 'vignetting effect', as both exhibit the same type of location dependency. The authors recommend that when image blocks are to be used for forensic investigations, they should be taken from the image centre before SPN extraction is performed in order to reduce false-positive rate.