There are a few ways to accomplish this.
First, there is a slightly hackish way to do it by setting the background image in css like this:
<canvas id="myCanvas" width="500" height="500" style="border:1px solid #000000;background-image:url('path/to/your/image.ext')">
</canvas>
This will work fine if you just want to display the image, however, I'm assuming that you want to actually manipulate it. In that case, check out this answer.