This paper addresses two general problems of imaging systems used for visual inspection and defect detection. On the one hand, the inspected object should be carefully removed in order to detect a potential defect or an anomaly. On the other hand, one of the features of imaging systems is that the noise level depends on the image intensity and so does the detectability of defects. In addition, due to the aging of the acquisition system (LEDs, Reflector), the intensity of the illumination decreases gradually over time. The present paper addresses jointly the impact of aging imaging systems and its ensuing impact on the detectability of a defect in the presence of linear nuisance parameters and signal-dependent noise.