ALT ATTRIBUTES

The alt attribute is used in HTML and XHTML documents to specify text that is to be rendered when the element to which it is applied cannot be rendered. In HTML 4.01, the attribute is required for the img and area element types. It is optional for the input element type and the deprecated applet element type.
Alternative text is especially useful in the following situations:
For people with low bandwidth connections, who may opt not to load graphics
For people using handheld devices
For people with disabilities who use assistive technology, such as refreshable braille displays or screen readers
For people using a pay per transferred data connection
Search engine optimization: most search engines interpret the meaning of objects by analysing their alt attribute
In the early years of Internet development, alternative text was particularly helpful to people using text-only browsers (like Lynx). Nowadays, even when graphical capabilities are taken for granted, alternative text is still highly appreciated by users with accessibility requirements and users looking for ways to optimize their network bandwidth use.

ANIMATION

Animation is the rapid display of a sequence of images of 2-D artwork or model positions in order to create an illusion of movement. It is an optical illusion of motion due to the phenomenon of persistence of vision, and can be created and demonstrated in a number of ways. The most common method of presenting animation is as a motion picture or video program, although several other forms of presenting animation also exist.

A zoetrope is a device that produces an illusion of action from a rapid succession of static pictures