WBMP type file has three kind of Extensions, but now WBMP Module can only open *.wbmp.
If it should register the other Extensions(*.wbm, *.wbp) in RegisterWBMPImage?
Are these really the same formats? Have you verified that GraphicsMagick can correctly read these files using a request like "wbmp:file.wbm" and "wbmp:file.wbp"? This format seems rather poorly designed in that it does not provide a good header by which the files can be automatically identified. As a result, a poorly named file might be read by accident by the WBMP reader, with unknown results.