Provided are a data collection method, a data collection system and a computer program for automatically collecting data in stages in classification. A data collection method is implemented by one or more processors connected to a sorting machine sorting articles to different sorting destinations. The method comprising: acquiring, by a processor, an identification code of an article from a reader provided on the sorting machine for identifying the article; acquiring, by a processor, image data of the article identified by the identification code from a camera that is attached so as to image the article after being read by the reader; storing, by a processor, the acquired image data so as to be associated with the acquired identification code.