Do you mean, the admin can set the bandwidth limit for every user account?
If that's the case, we need to store the statistics of the images time-based (minute, hourly, daily, weekly, monthly) so you can set more limits like (minute, hourly, daily, weekly, monthly).
Also note that statistics can be stored only for the images which are viewed via image URL and not via hotlinked, and for that, you need to do a custom setup.