{TASK] Fix errors in document to enable PDF rendering

The latex renderer cannot handle gif images and fails with
! LaTeX Error: Unknown graphics extension: .gif.
Convert the image to png for now.

Also remove an unused image, which would have the same problem.

One file contained a series of no-break space characters (unicode char
\u8:), which produced
! Package inputenc Error: Unicode char \u8:​ not set up for use with
LaTeX.