The best place to look for information about designing your graphics is the Apple Human Interface Guidelines. This document contains Apple's latest recommendations about designing applications for Mac OS X. Before you design an image, you should also check whether it is offered as a standard NSImage image. Using standard mages can save time and better improve consistency with the system. Opacity also includes several templates to help you create many images commonly used in applications, including buttons, cursors, and toolbar images. One great way to make the most of your image is to use variables. With variables, you can use one image file to generate several images to use in your project. You can use a boolean variable to make a button image with an enabled and disabled state, or a string variable to localize an image into several languages.