These images are in .gif format (web browsers do not support the .pgm format).
To convert them in the .pgm format, first right-click to save the images in
your local directory. Then open them using Irfanview (or your favorite software)
and save them again as .pgm images. Please note that some software packages do
not give you the option to save an image in .pgm format but Irfanview does.