Suggested sample usage of umbraco:Image
All attributes from the normal <img /> can be used. The idea then is to let different providers help generate the correct src attribute, based on the parameters given by the user. The reason for using an options attribute for input to the provider, is that you might want the server to render the image at a certain size, but not actually have the width attribute on the rendered image.
I have restricted it to images for now. It might be possible to create an umbraco:Media that would handle videos or sound as well, but I think images are the most valuable thing to operate with.
I have created some samples of how I think it could be used.