As described
here, the display size of included images can be specified as width or width plus height. I usually want to insert images, e.g. screenshots, at the same scale, not a the same size. In order to do that , I have to first look up the original size of each image and then calculate its scaled width.
I would like to suggest to extend DokuWiki's syntax for image insertion by a scaled value, i.e. in percentage of the original size. This might look like
{{wiki:dokuwiki-128.png%50}}
to display the image at half its original size.