You can use a combination of axes() to define where you
> want the image and imshow() to define the image. Use
> frame_on=False with axes(). You can pass a PIL image
> directly to imshow(), and that way you won't have to use
> imread, (although you'd have to use Image.open()).
If your logo is a fixed size in pixels, you can also use figimage to
place an unscaled image directly onto the canvas.
A wiki entry on matplotlib images + PIL would be useful.