If a picture on this blog is a flat image, and is geometrical in nature, it was probably created by me, using Geometer’s Sketchpad and MS-Paint. Sketchpad is available for purchase at http://www.keycurriculum.com/, and MS-Paint simply came pre-installed on my PC, as it does for most PCs which use any variety of Windows.
There are also many rotating images of three-dimensional objects on this blog, and those I make using a program called Stella 4d: Polyhedron Navigator. It is available at http://www.software3d.com/Stella.php, with a free trial download available, so you can try it before you decide whether or not to purchase the fully-functioning version I use.
Stella 4d allows the user the option of placing images on the faces of polyhedra, and sometimes I use images previously made, and sometimes blogged, using Sketchpad and MS-Paint. When this happens, therefore, it took all three programs to produce the final polyhedral images you see.
Because we have the same first name, I am sometimes confused with the author of Stella 4d, Robert Webb, but we are not the same person. I purchased these programs, and use them, but I did not write any of them.
Other images used are attributed where possible — such as the header-image for this blog, which is a Cyanide and Happiness cartoon. The software used to create this particular image is unknown to me, and was chosen by the cartoonist of that popular web-comic.