To retrieve type of a HGDIOBJ object call GetObjectType.
E.g.
GetObjectType( hGdiObj );
Possible return values taken from MSDN…
OBJ_BITMAP OBJ_BRUSH OBJ_COLORSPACE OBJ_DC OBJ_ENHMETADC OBJ_ENHMETAFILE OBJ_EXTPEN OBJ_FONT OBJ_MEMDC OBJ_METAFILE OBJ_METADC OBJ_PAL OBJ_PEN OBJ_REGION