Image Alt Text Vs. Image Title : What’s the Difference?
Image Alt :
Alt tag describe about images, It is alternative information about Image.
Alt text is meant to be an alternative information source for those people who have chosen to disable images in their browsers and those user agents that are simply unable to view the images.
Image title should provide additional information and follow the rules of the regular title: it should be relevant, short, catchy and concise (a title "offers advisory information about the element for which it is set"). In FireFox and Opera it showing like Tooltip.