I don't know what NAS stand for, but are you wanting to publish the database so that other users can access the pictures via a web browser?
If so, this can be done with instant or custom web publishing (IWP, CWP). You will want to research these approaches to see if they will work for you.
In any case, if the pictures are stored by reference, you will need to take care that the actual picture files are stored in the correct location. The exact location depends on how you plan share out the database over your network.
You should be able to use FileMaker's web viewer to acces your NAS files.