Hi...The required alt attribute specifies an alternate text for an image, if the image cannot be displayed.
The alt attribute provides alternative information for an image if a user for some reason cannot view it (because of slow connection, an error in the src attribute, or if the user uses a screen reader).
Note: Internet Explorer (prior version 9) displays the value of the alt attribute as a tooltip, when mousing over the image. This is NOT the correct behavior, according to the HTML specification.
Tip: To create a tooltip for an image, use the title attribute!