1. An image file editing method comprising: an input step of receiving a plurality of image files; an analysis step of analyzing a compression format of each of a plurality of images included in the plurality of image files; a display step of displaying a list of thumbnail images each of which corresponds to one of the plurality of images and displaying analysis results obtained in the analysis step together with the thumbnail images; a selection step of selecting images from among the plurality of images displayed in the display step; a determination step of determining, based on the results obtained in the analysis step, whether or not each image selected in the selection step is modifiable to have a compression format in which a first compression format is used for a first image region and a second compression format different from the first compression format is used for a second image region when the image includes the second image region; a compression step of compressing, using the compression format, an image that is determined in the determination step to be modifiable to have the compression format; and an output step of collectively outputting a plurality of images selected in the selection step as a single image file so that the single image file includes an image that is not compressed using the compression format in the compression step and an image compressed using the compression format in the compression step.