An image processing system which makes it possible to prevent an erroneous operation from being performed by an improper user. A console section of an MFP receives an operation from a user. A scanner reads an original to generate image data. A modem transmits the image data. A network interface receives an instruction for a reading and transmitting process for causing the scanner to read an original and then causing the modem to transmit image data generated by the scanner. When the instruction for the reading and transmitting process is received, a controller determines, based on a state of operation of the console section, whether or not the reading and transmitting process can be accepted. When acceptance of the reading and transmitting process is permitted as a result of the determination, the controller controls the scanner and the modem to perform the reading and transmitting process.