The disclosure provides a method, an electronic apparatus, and a computer readable medium of constructing a classifier for skin-infection detection. The method includes the following steps. A codebook of representative features is constructed based on a plurality of target-disease-irrelevant images. Transfer-learned disease features are extracted from target-disease images according to the codebook without any medical domain knowledge, where the target-disease images are captured by at least one image capturing device. Supervised learning is performed based on the transfer-learned target-disease features to train the classifier for skin-infection detection.