Why this is important: Assistive technologies such as screen readers can't read images; neither can search engines. Some sighted visitors might have images disabled for various reasons, or images might fail to load over a network. If alt-text is not given for images used as links, screen readers will read the whole URL instead, which is horribly confusing for listeners! The title= attribute (best practice) is used in Firefox for mouseover (alt= is used in IE); many low-vision users benefit from having this available.