An image decoloring apparatus includes a reader configured to read an image on a sheet to acquire image data, a storage section configured to store the image data acquired by the reader, and a first heater configured to heat the sheet. The apparatus further includes a difference extractor configured to extract difference image data based on first image data read from the sheet before it is heated by the first heater and second image data read from the sheet after it is heated by the first heater. The apparatus additionally includes a setting section configured to set a password required to access the difference image data.