In response to a print instruction instructing a printer to print an image being made with respect to a general-use printing program implemented in an operating system of the information processing device, the information processing device uses a supporting program to obtain an image size of print data subject to printing based on the number of vertical dots, the number of horizontal dots, and print resolution of the print data. Further, the information processing device obtains second size information indicating a sheet size included in a print setting and determines, by comparing the image size the sheet size, whether the sheet size conforms to the image size. When determining that the sheet size does not conform to the image size, the information processing device performs a warning process of displaying a warning message using a user interface.