This page demonstrates rolling over both an image (small gif), and link text in a div tag box (Small div) to toggle the visibility of a big image (big gif).
The visibility of a big image (big gif) is controlled with the visibility property/value (visible and hidden) attached to the img.hid rule/style.
The CCS styles for this page are located in the <head> tag of this page, so just view the page source code to see what's going on.