In this directory/folder, several images of squares with (and also without) a piece on it can be found. These can be used for displaying positions of chess or variant chess games and problems.
Here, you see a list of all the images. A few appear more than once under different filenames.
Many of these images are of use in combination with the FFEN-to-HTML tool or the ffen2diag tool, which help to add chess (variant) setups to webpages.