I think you've been misled -
Here's some text from XP's MSPAINT Help:
To specify opaque or transparent drawing
To draw an opaque image, on the Image menu, click Draw Opaque and make
sure a check mark appears next to it. Selecting Opaque specifies that the
existing picture will be covered by the white background of a selected
area in Paint.
For example, in the image at the left, notice that the small dotted box
includes a white background around the green box. Also notice that the
white background covers the larger image behind it. To draw a transparent
image, on the Image menu, click Draw Opaque and make sure the check mark
does not appear next to it. Turning off Opaque specifies that the
underlying pictures will be visible through the background of a selected
area in Paint.
For example, in the image at the left, notice that the small dotted box
is clear and the green box displays inside it. Also notice that the
content of the image behind it is visible right up to the green box.
Related Topics
I think it just means what happens when you overlay an image.
--
Bah, and indeed Humbug.