A method of processing B-scans acquired by an OCT imaging system to generate correction data for compensating for axial displacements between B-scans caused by a variation in distance between the OCT imaging system and an imaging target, and to generate a reliability indicator indicative of a reliability of the correction data. The correction data is generated by determining, for each pair of adjacent B-scans, a respective indicator of an axial shift between respective representations of a common ocular feature in the adjacent B-scans. The reliability indicator is generated by: calculating values indicative of speeds or accelerations of the imaging target relative to the OCT imaging system when pairs of B-scans were acquired; where at least a predetermined number of calculated values exceed a threshold, setting the reliability indictor to indicate that the correction data is unreliable, and otherwise to indicate that the correction data is reliable.