The ZW7A only accomodates JPEG files. JPEG files (or .jpg files) are the most common image type and are the default file type for the vast majority of digital cameras.
If the customer does not know what type of files he or she has click here.
If your customer is sure that he or she has JPEGs, but they still will not display, Have them unplug and replug the unit from its power source. If that does not work click here.