MacDraw Pro 1.0 / 1.5v1 does not support changing the white pixels of a bitmap, such as a scanned image, from white to transparent. Thus, placing a scanned image over another object will mask out the other object, rather than seeing through the "blank" areas of the scan to the object beneath. There are two workarounds to this problem. The following information applies to black and white (line art) bitmaps. Color/grayscale scans cannot be made to have transparent pixels.
Workaround #1
Resave the scanned image in another file format. For example, the AppleScan and Ofoto scanning software save the blank areas of a scan as white pixels to a PICT file, but as transparent pixels to a TIFF file. Other scanning sofware may behave similarly.
Workaround #2
MacDraw II 1.1 allows changing the background color of a bitmap to transparent. Thus, one workaround to this problem is to open the bitmap in MacDraw II, save, then Open/Place the file in MacDraw Pro.