How to position images with stretch = Uniform when children of a canvas from a behavior?

Question

I have a behavior which adds Images as children of a canvas:

 private static void OnSourceChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            var behavior = d as ImageCanvasBehavior;
            if (behavior == null)
                return;

            // The AssoicatedObjec is a Canvas.
            Canvas canvas = behavior.AssociatedObject as Canvas;
            if (canvas == null)
                return;

            canvas.Children.Clear();

            CroppedBitmap b = (CroppedBitmap)e.NewValue;          

            Image img = new Image();
            img.Source = b;
            img.Width = canvas.ActualWidth;
            img.Stretch = Stretch.Uniform;

            canvas.Children.Add(img);
        }

The img is added about midway of the horizontal and vertical of the canvas. How can they be positioned to the top-left of the canvas?

TIA

Edit#1 First attempt at a visual tree:

Edit#2 I believe this to be wrong...Only the image should be showing, not all the black space above and below the image and the image should not be cut off.

Answer 1

Use the attached property:

        Image img = new Image();
        img.Source = b;
        img.Width = canvas.ActualWidth;
        img.Stretch = Stretch.Uniform;
        Canvas.SetTop(img, 0);
        Canvas.SetLeft(img, 0);