I think I have it, you needed 2 cls.
One to clear the backbuffer.
Then flip
Then another to clear the backbuffer again.
One to clear the backbuffer.
Then flip
Then another to clear the backbuffer again.
Graphics3D 800,600,32 SetBuffer BackBuffer() image=LoadImage("space08.png") exit1=False exit2=False DrawImage image,0,0 Flip Repeat If KeyHit(57) Then exit1=True Until exit1=True FreeImage image Cls Flip Cls Repeat If KeyHit(57) Then exit2=True Until exit2=True