System and method for measuring distances in an image. An image is received that includes curves corresponding to one or more objects in the image. Multiple curves in a specified region of interest (ROI) in the image are detected, where the ROI has a specified direction. Each curve includes respective curve points. A convex hull is determined based on the respective curve points. One or more candidate antipodal point pairs of the convex hull are determined. A first point pair of the one or more antipodal point pairs is selected based on one or more specified constraints. A clamp angle corresponding to the first point pair is determined. A distance between the first point pair along a direction specified by the clamp angle is determined. The first point pair, the distance, and the clamp angle are stored. Calibration information may be applied at any point during the process.