Very Simple Captcha: Generate images for CAPTCHA validation

This class can be used to generate images for CAPTCHA validation.

It generates an image with a random validation text. The image has some lines and shapes rendered in a different color to obfuscate the text.

The width and height of the image, and the length and the font of the text are configurable details.

The image text is stored in a session variable for posterior validation.

The generated image is served as the current script output in the JPEG format.