When configuring SharePoint with Web Services Gateway you will need to add each site individually in the configuration wizard so that it is accessible in Field Supervisor. Whether your SharePoint environment is to create multiple Site Collections or to create multiple within a Site Collection. Once configured all document libraries, including picture libraries, will be visible in Field Supervisor. The credentials used in the app when adding the server will control which libraries you will be able to access in the App.
Below is a diagram to help explain the different possible SharePoint environments.