1. A method comprising: supplying a character code to a text rendering engine being tested to cause the text rendering engine to render a character corresponding to the character code, identifying a graphical reference image for the character, wherein the graphical reference image was produced by a source known to produce correct images; presenting the graphical reference image and the rendered character on a bitmapped display screen of a computer system to facilitate a visual comparison between a visual representation of the graphical reference image produced by the source known to produce correct images and a visual representation of the rendered character produced by the text rendering engine to be tested; receiving, by the computer system, user input indicating user evaluation of the graphical reference image and the rendered character, the user evaluation being based on the comparison between the visual representation of the graphical reference image and the visual representation of the rendered character, the user evaluation identifying one or more differences between the graphical reference image produced by the source known to produce correct images and the rendered character produced by the text rendering engine to be tested; and storing, by the computer system, the user evaluation in a database for subsequent debugging of the text rendering engine.