You have a great start for 1.1, heres a few suggestions, let users specify the number of thumb nails and size of thumb nails on each preview page, for ease of use you should scan the directory and sub directory that the user chooses to be the root image directory for example when your program asks the user for the directory that the images are located in your program should check any sub directorys as well. Make better use of the side bar that lists the current directory you are in