I am using Blender Version 2.78, in the default layout I did the following:
- 1 to go into front view
- space to enter command: allign camera to viewport
- n to open the box on the right
- selected image>movie clip
However no movie clip showing up, I tried both orthographic and perspective mode, inside and outside the camera. When I open an image as a background, it shows up on pressing 7 on the numpad. The movie clips I tried to open as background images already worked in blender inside the video sequence editor.