After a number of false starts, I have managed to get images to display in the wiki. I placed the images within a folder of the wiki repository, i.e. wiki/eggref/4/pstk-images/*.png and then tried to find the correct reference to place in the 'image' tag.
None of the relative urls I tried worked: [[image:/eggref/4/pstk-images/pstk-conversion.png|ALT]]
[[image:pstk-images/pstk-conversion.png|ALT]]