Every few days I have to update a large collection of image files that are stored on defaultexternal. I build a list of the image file names and then use httputils to download the files from web server. It works, but just seems inefficient to download every single file in the list when actually only a few are new or changed. I would like to somehow compare the existing image on the device to the same image file on the server, and only download those that have changed or are new (present on the server but not present in defaultexternal). Determining the new files is no problem, but I don't know the way to compare existing files to the files on the server do determine if they have changed.