Performing index printing to print a plurality of images on a sheet

A printing device comprising:

• a print engine configured to perform an index print to print a plurality of thumbnail images on one sheet, the plurality of thumbnail images corresponding to respective ones of a plurality of files stored in an external memory;
• and
• a controller configured to control the print engine, the controller being configured to perform:
• determining a type of each of the plurality of files stored in the external memory;
• setting each file determined to be an image file as a first reference file to be used to generate a thumbnail image for the index print;
• converting each file, which is determined as a non-image file and includes a page description language, to an image file representing contents of the each file by interpreting the page description language included in the each file;
• setting the image file converted from each file, which is determined as a non-image file and includes a page description language, as a second reference file to be used to generate a thumbnail image for the index print;
• generating a print command for the index print to print, on the one sheet, the plurality of thumbnail images including the thumbnail image based on each image file set as the first reference file and the thumbnail image based on each image file set as the second reference file;
• and
• controlling the print engine to print an index image according to the print command so that the plurality of thumbnail images including the thumbnail image based on each image file set as the first reference file and the thumbnail image based on each image file set as the second reference file is printed on the one sheet.