You can import 2D images, drawings, or sketches into your orthographic cameras as image planes. Image planes are a component of the camera that let you place an image file in the view of the camera view which you can use as a visual reference as you sculpt your 3D forms. An image plane only appears in the camera to which you connect it. You can adjust the transparency of the image so it doesn't block your view of the mesh or adjust the Depth property for the image plane so it appears behind the object.