Red China in Tibet by MakinMagic

I use a program called Ultra Fractal which is primarily designed for rendering fractals but can be used to create many forms of mathematical/algorithmic art.
Anyone (who can program) can write their own formulas/algorithms for Ultra Fractal.
Since UF4 (I think) the program has also had the functionality to import images and manipulate them e.g. to map them into fractals etc.
I'm a programmer by professin and wanted an easy and optimum way to do seamless tiling (e.g. for texturing objects) and UF presents an easy way to test such algorithms.
The method used was inspired by the (manual) method suggested in some Photoshop tutorials for creating seamless tiles which I simply extended to allow a seamless tiling of 2 images such that either of the 2 images can go at any position within a rectangular tiling - as a minimum this effectively means that 16 variations are actually required of each base image i.e. 32 in total - these can either be pre-rendered or created on-the-fly from the two base source images.