A whole slide image (WSI) is a digitized microscopic image that is particularly useful in histochemistry and cytochemistry. Several WSI scanners have been introduced in Japan and all use their own native format. Thus, there is basically no interchangeability. However, the Digital Imaging and Communications in Medicine (DICOM) standard format for WSI has been available since 2010. In this review, the configuration and differences among the native WSI and DICOM formats are examined, and the advantages and issues of DICOM standardization are discussed.