I tested all versions in portage, here that option does not work. Reproducible: Always Steps to Reproduce: wget --wait 1m --random-wait http://gentoo.org Actual Results: It just download every time without delay.
On an interactive shell it works. You need to do the same in a script file.
Ops, seems that is related to [image/jpg] mime not everything.
For that to work you need three things on the command line: --wait N --random-wait and more than one URL. If you are going to script this anyway to have separate wget calls for singular URLs, then you might as well script a sleep time between calls instead of relying on wget to do it. If you want this behaviour changed or better explained, please complain upstream at the [URL].
See the source code at src/retr.c around line 1151.