The last page shows how the front cover was made. (Click to start dowloading the page in another window.)
The whole thing really was very simple. 2 photos I already possessed, 2 pages of paint splodges, 2 cheapish graphics packages (you could get by with Paint Shop Pro), an ink jet printer and a scanner (or a camera). There is a final element, experimentation. Just trying things out, seeing what happens, working out why, and remembering for next time.