1. A method of constructing a classifier for melanoma detection comprising: constructing a codebook of representative features based on a plurality of target-disease-irrelevant images; extracting a plurality of transfer-learned target-disease features from a plurality of target-disease images according to the codebook, wherein the target-disease images are captured by at least one image capturing device; and performing supervised learning based on the transfer-learned target-disease features to train the classifier for melanoma detection.