image courtesy of Sarefo under GNU licensing http://commons.wikimedia.org/wiki/User:Sarefo
The technique is called stacking and Thystine used Helicon Focus to achieve the effect. Helicon Focus Software reportedly "...... creates one completely focused image from several partially focused images by combining the focused areas. The program is designed for macrophotography, microphotography and hyperfocal landscape photography and solves the shallow depth of field problem........"
Alternate software which has received great reviews from some other contacts on Flickr is "Zerene Photostacker" . Their website provides a most effective explanation of the process and combined with a great Video has encouraged me to place photo stacking on my bucket list to be done sooner rather than later.