Use the New Bitmap Layer 
 
button to create an empty bitmap layer. You can create as many bitmap layers as 
you like. This enables you to include many different images in a single model. 
You can only display one bitmap layer at a time.
To create a bitmap layer:
By default, each bitmap layer you create is:
A default colour palette, comprising ten basic colours, is 
associated with each empty bitmap layer you create; this is displayed below the 
2D and 3D views.When a bitmap layer results from an imported image file, a 
palette containing the colours used in the imported bitmap is 
displayed.
If you are working in the 3D view, click the Display Bitmap 
 button 
on the 3D View toolbar to display the active 
bitmap layer.