Add Images to a Button
You can put a primary image and an alternate (hover) image on a button. The alternate image appears when you hover your mouse over the button. The images can be in .bmp, .jpg, .png, or .ico format. The image files are stored in the Template Image path set up under Universal Preferences in System Administrator.
Hover images must be named after the primary image with a suffix of _hov. For example, if the primary image is named anteriorchamber.bmp, the hover image must be named anteriorchamber_hov.bmp.