Non-destructive evaluation of structures is a key procedure in operation of aircraft structures, necessary to maintain their quality and integrity. Numerous non-destructive testing (NDT) techniques have been adapted to inspect aircraft structures and are currently used according to appropriate protocols. However, many of them provide only qualitative results, such as the D-Sight optical NDT technique used for inspections in aviation. In this study, a concept of improvement of the D-Sight technique is proposed by means of appropriate experimental program and processing procedures applied to the resulting images from inspection. It was demonstrated that appropriately selected processing methods may allow assessing damage quantitatively and improve the overall sensitivity and applicability of a given NDT technique.