Greetings, which model iPad do you have? If possible, can you connect your iPad to an external monitor and reply with the results as to whether the problem continues to exist on the external display?
The iPad 2 does have to ability to connect to an external monitor, if you do not have the cable and monitor available then I suggest going to the the Genius Bar and having them try. At least in that way you can determine whether the display in the iPad is defective or if it is a mainboard problem.
You mention that the "shadow" quivers, does that mean it changes in size or intensity? Is the edge of the shadow in a straight line? Is the edge of the shadow sharp or does it gradually blend into the normal part of the screen?
OK, I was trying to determine whether the backlight was to blame but it seems you still need to try the external monitor. If the problem vanishes on the external display then the iPad's display is defective. Repairs can be made by an experienced technician to replace the LCD panel but the cost could exceed the value of the iPad itself.
I need to leave on a service call. You can reply here with the results of your visit back to the Genius Bar if you like. Dan