The "sources" of the images are the PowerPoint (.pptx) files. The actual image
(.png) files are obtained as follows. Each file consists of a single slide,
whose area of interest is delimited by a dashed rectangle. Take (something like)
a screenshot of the area just inside the dashed rectangle, and resize it to W
pixels wide, preserving the width/height ratio of the image, where W is about
800 pixels divided by 13.33 inches (the width of a slide in these PowerPoint
files) and multiplied by the width of the dashed rectangle in inches. In other
words, we want the whole slide to correspond to about 800 pixels in the manual,
so that the relative sizes of the pictures are preserved. Save the result in PNG
format.
