Mouse Move Flicker

I'm betting I'm just tired and over looking the obvious but this is driving me nuts... basically I have a circle clip defined that has an image 'behind' it. I want to be able to move the image around to adjust what is visible throught the circle clip area. Anyway, I got it all working except when I move the image it flickers like mad.
 
Here's the code:
        private void Page_MouseMove(object sender, MouseEventArgs e) {

             if (Mouse_LeftButtonDown) {
                double currentX = (double)imgUpload.GetValue(Canvas.LeftProperty);
                double currentY = (double)imgUpload.GetValue(Canvas.TopProperty);

       &n ...