I am using StretchImage to put a bitmap on the display and there is a parameter on the end called Opacity.
The Microsoft website says this about it.
The bitmap’s degree of opacity. A value of 0 (zero) makes the bitmap completely opaque (not transparent at all); a value of 255 makes the bitmap completely transparent.
If I use 0, nothing is shown. If I use 255, I see the bitmap but the there is a shadow left by something that is drawn in black on a white background. It’s a bit like a burn in effect but it is clearly not that. Pausing the display update and the shadow remains.
Any other value in between and it gets worst for the shadow effect.