You are reading an outdated manual
In this link download vym.pdf 2015/11/05
https://sourceforge.net/projects/vym/files/2.5.0/
Quoted from:
View Your Mind
Version 2.2.4
Uwe c Drechsel
April 8, 2013
Best regardsImages
The easiest way to add an image to a branch is by dragging it e.g. from a webbrowser to
the mapeditor while a branch is selected there.
You can also add an image to a branch by opening the context menu of the branch. Right
click the selected branch, choose ”Add Image”. A dialog window enables you choose the
image to load. 3 While an image is selected in the dialog, a preview of the image is
displayed. It is also possible to select multiple images...
Resizing images has been added to /vym in version 1.13.20. Later versions will include
more functionality like changing its z-value (put it into background) etc.
joejac