Using PictureFrames as background bitmaps
->

* Start the PictureFrame command
* Locate the image you wish to use
* Place the plane.
Once the image is placed, you can transform the plane(move/scale/rotate…) like any other objects in rhinoceros, It seems that the PictureFrame is rather more convenient than BackgroundBitmap.
The PictureFrames display in all viewport mode, even in wireframe mode.

adjust transparency & intensity
good tip.