I guess you do not generate your world programmatically. You will need to find an editor suitable for this job, or write one yourself.
I can advice you to use R.U.B.E which lets you create your Box2D worlds and attach images to the bodies. You may then export the scene via JSON which fits very well to javascript.
The rendering of those images attached to bodies will be a custom job. As well as the importing of the scene if there is no loader for box2dweb yet.