What is the difference between blocks of the BT_RasterPicture and BT_VectorPicture type?
The part of the image that the BT_RasterPicture encloses is not recognized, and the block is exported "as is." Properties of this block type are represented by the RasterPictureBlock object.
Blocks of BT_VectorPicture type may appear in the layout only if a 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 VectorPictureBlock object.
If it is not crucial to differentiate these two types of blocks, you can set the IPageAnalysisParams::DetectVectorGraphics property set to FALSE in order to recognize all pictures as BT_RasterPicture type and remove any possible picture overlapping.