Though used mainly for generating HTML, you can also generate any other file such as an Image with PHP. Normally you would use special libraries such as Imagemagik or GD to assist PHP in generating Images, however, for this example we do no manipulate any image data, so we will not be needing any special PHP libraries.

Here's a class I wrote as an example of implementing the Vigenere Cipher. It is based on the description of the Vigenere Cipher at WikipediaThe Vigenère cipher is a method of encryption that uses a series of different Caesar ciphers based on the letters of a keyword. It is a simple form of polyalphabetic substitution..