Image can't be used as a return type for WCF? [Closed]

Question

I have the contract defined as:

public interface IService1    {
        [OperationContract]
        Image UploadOneImage();
}

I always get exception on client side. then I switch to following:

 public interface IService1    {

             //serialize Image to byte[]
            [OperationContract]
            Byte[] UploadOneImage();
    }

then no exception, so Image can't be returned from WCF?