Image not displayed on the System.Windows.Controls.Image control

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Silverlight

Referring to https://msdn.microsoft.com/en-us/library/system.windows.controls.image.source(v=vs.110).aspx[^] I wrote a piece of code below in my SL project. My purpose is to create an Image control. This piece of code is in my MainPage.xaml.cs. The images are stored in \Images\, which is parallel to the MainPage.xaml.cs under the project tree. Unfortunately, the images do not display. What's wrong in my code (I guess it is uri specified here). Thanks.
The related code is below:

spNewItem.Children.Add(BuildImageButton(@"Images\fan1.ico", h, w));
...
        public System.Windows.Controls.Image BuildImageButton(string source, int h, int w)  {
            System.Windows.Media.Imaging.BitmapImage bi = new System.Windows.Media.Imaging.BitmapImage();
            bi.UriSource = new Uri(source, UriKind.Relative);

            Image img = new Image { Width = w, Height = h, Source = bi};
            img.HorizontalAlignment = System.Windows.HorizontalAlignment.Left;
            img.Margin = new Thickness(5, 0, 0, 0);
            return img;
        }