Sketching software design models is a common and intuitive practice amongsoftware engineers. These informal sketches are transient in nature unlesstransformed into a formal model that can be reused and shared. Manualtransformation, however, is time-consuming and redundant, and a method toautomatically transform these sketches into a permanent and formal softwaremodel is lacking. This study addresses this gap by creating and testingSketchToPlantUML, a sketchrecognition and transformation tool that reduces theeffort of manually transforming static, sketched UML Class Diagrams (CDs) intoformal models. The artefact uses the OpenCV library to preprocess images,segment UML elements, identify geometric features, classify relationships andtransform the output into the equivalent, formal PlantUML model. Tested againsta dataset of 70 sketched CDs, the artefact achieved overall Precision and Recallvalues of 88% and 86% respectively, scoring highest on classes (0.92 / 0.96) andlowest on association relationships (0.76 / 0.76). While the approach providesinsight into image processing and object recognition using OpenCV, a morerobust and generalised solution for automating the transformation of UMLsketches into formal models is needed.