Find the file app/routes/route.image.php
From line 252 you'll see the embed codes. You can literally remove the chuck of code relating to the embed code that you don't want.
Once done, save the file and put it into the app/routes/overrides folder leaving the original file intact.
That will work but ideally you should make a copy of Peafowl and edit that instead.
It doesn't actually restrict the users though as they could still easily work out what the full image embed code should be.
BTW make sure you a decent text editor like
Notepad ++