The present contribution introduces a method for assessing the load bearing capacity and failure mode of real historic masonry walls subject to in-plane loading conditions. Following successful image acquisition, the Segment Every Grain Method (SEGM) is used to identify and delineate individual blocks. These blocks serve as initial inclusions in a distance fields-based morphing procedure. The mortar joints’ spatial information is lumped onto zero thickness interfaces by exploiting the notion of Medial Axis. By assuming blocks to be infinitely strong and rigid, the failure loci are restricted to the mortar joints, to which a Mohr-Coulomb frictional behavior is assigned. Assuming small displacement kinematics, perfectly plastic post-peak behavior and an associated flow rule allows the final problem statement to be framed as a linear programming problem and solved accordingly. The presented approach carries a low computational cost and enables the rapid evaluation of “what-if” loading scenarios on geometries derived from real historical masonry walls. This is further illustrated with an example.