You need one NTB per display image.
The image from one NTB can be sent to more than one display screen using either:
VGA splitting is suitable if the NTB-to-screen distance is less than 50m.
VGA over Cat 5 is suitable for distances up to 500m.
See our partners Smart-e.co.uk for more information.
For distances greater than 500m, use Channel Manager i.e. One NTB clones itself off another across the network. You need one NTB per site.
Channel Manager does, however, allow for some local customisation of the content so, for example, a welcome message can be different at the different sites but everything else is the same.