An acquired image is analysed to determine a test outcome value. A shape template for a test structure is provided to identify a position of a target measurement region on the test structure. A mapping defining a transformation of the shape template onto the image frame is determined. A mapping is determined and it is determined if a first matching condition based on first displacements of one or more edges identified in the image frame relative to the shape template is satisfied for the mapping. When the mapping satisfies the first matching condition and a second different matching condition based on second displacements of one or more edges identified in the image frame relative to the shape template, a verified image of a test structure is established. In the verified image of the test structure a target measurement region is identified. A test outcome value is determined by analysing the target measurement region.