Simple question on "images" and overlaying

I have an image component on a form that I am constantly overlaying with different images. (bitmaps).  The images sometimes don't copy cleanly (for example, sometimes when I copy a notepad window, some text is missing, etc.) Should I be clearing this out before laying a 2nd image over the first? How do I clear it, as I am guessing that is what's causing the problems?
                 Thanks