Viewport view of Image???

If I’ve inserted a 2D image of a car into Blender, but its the back of the car, and I want to ensure the the view in the viewport of the image is from the back then what on the numpad number do I press for the view to change to the rear of the 2D image?

numpad 1 = front
Ctrl + numpad 1 = back
numpad 3 = left
Ctrl + numpad 3 = right
numpad 7 = top
Ctrl + numpad 7 = bottom