Can anyone tell me the best way to store multiple images related to a single mongo document?

My use-case is that I have a “user” doc in the “profile” collection. This document has metadata about the user(email address, phone #..).  

Then we have the ability to upload multiple images about a user. 

We are using GridFS to store the images in the files collection, and I get back the id of the uploaded image from GridFS. 

What is the best way to relate that image object back to the user object that uploaded it? I can put the User’s ObjectID in the metadata of the Image Object….or I can put the ObjectID in the User Doc(and create a collection of Images).

We are using the C# driver…so if anyone has any examples of my use-case…that would be great.

Thanks
MJD