A method to assess a subject diagnosis is provided. The method includes receiving an image from an image-capturing device, the image comprising an area of interest in a test cartridge, and finding a border of the area of interest of the test cartridge and applying a geometrical transformation on an area delimited by the border of the test cartridge to bring the image of the area of interest in the test cartridge to a selected size and a selected shape. The method also includes identifying a target region within the area of interest of the test cartridge, evaluating a quality of the image based on a characteristic feature of the target region, and providing commands to adjust an optical coupling in the image-capturing device when the quality of the image is lower than a selected threshold.