The Background Image panel allows you to choose an image that will be displayed as reference in the active view.
To open it, select the Image Plane command from the View menu.
Press the Browse button to choose the reference image.
You can so use any sketch to help you draw lines and curves of your project.
Note: This image will not be used for the final rendering, in which case you should use the Image shaders from the Background shader class.
If you want to remove the image as background of a view, just switch off the Visibility check button.
Ref. Space (Reference Space) should be used to determine whether the image size should be independent from the zoom factor (View) or bound to the zoom factor (3D).
The Position section offers three options: Free if you want to freely position the image within the view, Center if you want it centered, Fit to adapt it to the entire view.
The Origin section lets you set the position of the image origin in case you have chosen the Free option in the Position section.
Adjusting the Horizontal and Vertical value modifies size of the image plane. Leave the Keep aspect ratio option switched on if you want to maintain proportions.
The image plane can be rotated by simply setting the Angle degree in the Rotation section.
Press Apply to display the image plane or to update settings without closing the panel or OK if you also want to close the panel.