D-Link DNS-320L User Manual page 204

Section 4 - Configuration
Under the Select Photo section, click the Browse button to search your
computer for photos.
If you wish to add more than one photo, repeat the process or hold the Shift key
to select a range of photos, or the Control button to select several individual
photos.
Click the Open button to add them to the Album.
D-Link ShareCenter DNS-320L User Manual 198