Systems and methods for iteratively computing an image registration or an image segmentation. The registration and segmentation computations are driven by an optimization function that includes a similarity measure component whose effect on the iterative computations is relatively mitigated based on a monitoring of volume changes o volume elements at image locations during the iterations. There is also a system and a related 5 method to quantify for a registration error. This includes applying a series of edge detectors to input images and combining related filter responses into a combined response. The series of filters are parameterized with a filter parameter. An extremal value of the combined response is then found and a filter parameter associated with said extremal value is then returned as output. This filter parameter relates to a registration error at a given image 10 location.