To hide the border frame of added images, use one the following code fragments:
OdDbRasterVariablesPtr pRVars = OdDbRasterVariables::openRasterVariables(pDb->database(), OdDb::kForWrite);
pRVars->setImageFrame(OdDbRasterVariables::kImageFrameOff);
or
OdResBufPtr val = OdResBuf::createObject();
val->setRestype(OdResBuf::kRtInt16);
val->setInt16(0);
pDb->setSysVar(OD_T("IMAGEFRAME"), val);