The authors propose a method and metric to quantify the consumer confusion between leading brands and copycat brands that results from the visual similarity of their packaging designs. The method has three components. First, image processing techniques establish the objective similarity of the packages of leading and copycat brands on the basis of their colors and textures. Second, a perceptual decision task (triangle test) assesses the accuracy and speed with which consumers can identify differences between brands from rapidly (300 milliseconds) flashed images of their packages. Third, a competing accumulator model describes the buildup of evidence on each of the alternative brands during consumers’ perceptual decisions and predicts the accuracy and response time of brand identification. Jointly, these components establish the impact of copycat packaging’s visual features on consumer confusion. The method is applied in a test of experimentally designed copycats and market copycats in 15 product categories. A three-tiered metric (“copy alert,” “copy watch,” and “copy safe”) establishes the extent to which copycat brands imitate the package designs of target brands and identifies which visual features are responsible.