Is there a way to assign a default Avatar to all user created groups within a particular Category?

For Profile Types, there's an option to add default avatars to each profile. I don't see such an option to provide default avatars for Groups created by users. Selecting an avatar in the back-end for a Categories is available.

The Category Custom Field: Avatar, seems to indicate providing default avatars is possible based on the options provided: Avatar uploads, Avatar gallery selection and Use gallery button options. I don't see anywhere to add default Avatars, however. It appears that only the user upload option is actually available.

Did I miss how to accomplish adding default avatars for Groups within a Category? If it's not possible to limit a group's creator to selecting from only a few default avatars, I'd like to have the Group Avatar be the same as the associated Category Avatar and not provide the user the ability to choose another. How can this be accomplished?