Images4Education

Use the alt attribute to provide text for visitors who, for whatever reason, can’t see the images in your document. This includes visitors using browsers that cannot display images or have image display disabled, visually impaired visitors, and screen reader users. Alt text is to be used instead of an image, not as additional information.

And don’t use the alt attribute for text that you want to appear as a tool tip. It’s not the way it was meant to be used, and as far as I know, it only works like that in Internet Explorer for Windows and in Windows versions of the ancient Netscape 4.*. No Mac browsers display alt text as a tool tip.

The title attribute can be used with all elements except for base, basefont, head, html, meta, param, script, and title, but it isn’t required for any. Maybe that’s why it’s less clear when to use it. Use this to provide additional information that is not essential. Most visual browsers display title text as a tool tip when the element is hovered over, however it is up to the browser manufacturer to decide how the title text is rendered. Some will display the text in the status bar instead. Early versions of Safari did this, for instance.