What is the difference between BT_RasterPicture and BT_VectorPicture blocks?
The part of the image enclosed by a BT_RasterPicture block is not recognized, and the block is exported "as is." Properties of this block type are represented by a RasterPictureBlock object.
Blocks of type BT_VectorPicture may appear in the page layout only if the page has been analyzed with the IPageAnalysisParams::DetectVectorGraphics property set to TRUE. Usually, background pictures are recognized as the blocks of this type. Additional properties of the blocks of this type are accessible via the corresponding VectorPictureBlock objects.
If it is not crucial to differentiate these two types of blocks, you can set the IPageAnalysisParams::DetectVectorGraphics property to FALSE in order to recognize all pictures as BT_RasterPicture blocks and remove any overlapping.