This paper describes the process of extracting and classifying defect in optical photomask images. It describes photomask defect extraction which is the preprocessing of classification. In addition, it describes not only how to classify defect into false, particle on glass, and pattern defect but also how to classify pattern defect into spot, Cr extension, bridge, MoSiN bridge, pinhole, clear extension, break, and stitching. Also, how to classify a particle according to its size is presented.