This is a small text description of the image that can be of use to visitors but should {b]always be included for the benifit of the search engines.

When possible, captions are displayed under the image in italics. For images that are ´wrapped´ the caption can not be displayed visibly but will appear as if ´wollover only´ was checked (see below)

Rollover Only
This hides the caption so that it isn´t visible on the page but if the visitor holds their mouse over the image it will pop-up. The search engines look for this type of text (called an "Alt" tag) so if you don´t want guests to see the caption but still want to maximize the effect for the search engines - include a ´rollover only´ caption.