From Scantegrity Wiki
Invisible Ink Symbol Generator Module
The Invisible Ink Symbol Generator (IISG) Module processes symbols and produces an image of the symbols with a background of reactive ink and a foreground (font color) or non-reactive (dummy) ink. The images produced by this module are embedded into ballot files that are printed on an invisible ink-capable printer. The generated images is straightforward, but the module has a number of extra functions to increase the security properties of the printed ink.
We need a module or set of functions that can takes font attributes, height/width, text data, and threshold values, then produces a bitmap where each pixel color is a random value within the given threshold for that pixel type.
Another desired functionality is an overlay for a whitespace grid over an image with grid squares being a specified height and width in pixels, and the lines being a specified thickness.