I waited but no body answered this question so, after seeing all properties of ManagementBaseObject I found that there is a property named Service which is different for scanners. In scanners the value of Service property is usbscan while in cameras it is usbvideo. eg. you can do something like this
if (mbo.Properties["Service"].Value.ToString() == "usbscan")
{
//then it means it is a scanner
}
else
{
//then it means it is a camera
}
note: The main question was that how can we differentiate between a scanner and a webcam because they both use same GUID.