Cell CAPTCHA: Generate and validate CAPTCHA created with divs

This class can be used to generate and validate CAPTCHA text that is created using colored div's and is stored in session variable.

The class renders simulated text by shading certain table cells that show the text in a given color and no actual image is generated.

It can also verify whether a text submitted by the user matches the CAPTCHA text. The verification can be case sensitive or insensitive.