Animated Simple CAPTCHA: Generate a CAPTCHA validation animated image

This class can be used to generate a CAPTCHA validation image that is animated.

It generates a random text that is stored in a session for posterior user validation.

The class renders a series of frames with the text obfuscated by animated letters, grids and optional random fonts.

The user can read the text when the animated frames are displayed but robots will have difficult to figure what the text is.

The class can also validate the text submitted by the user against the value stored previously in a session.