1. A method of operating an image display apparatus, comprising: receiving a first input signal; displaying a first image on a display based on the first input signal; receiving a second input signal; generating a first thumbnail image based on the second input signal; displaying simultaneously a first thumbnail list including the first thumbnail image and a second image based on the first input signal in a compact-view mode, determining whether an error exists in updating the first thumbnail image; and if no error exists, or if an error exists and an error ratio of an updated second thumbnail image is less than a reference value, displaying the updated second thumbnail image in the first thumbnail list based on the second input signal; and displaying a second thumbnail list including a plurality of thumbnail images in full-view mode on the entire display according to a user input, wherein the reference value is set differently for the compact-view mode and the full-view mode.