Add simple image layers to MapBox / Leaflet?

Is there an easy way to add simple image layers (with no, or very limited, GIS data) to Mapbox and/or Leaflet?

Google maps seems to have the ability to add custom layers, simply by attaching the SW and NE corners to points on the image to points on the map

I thought that MapBox or Leaflet would have similar functionality, but I'm struggling so far.

I (presumptuously?) assumed that TileMill might allow me to import a non-GIS labelled image and drag and drop it to the correct position - much as you might align two Photoshop layers. However, I seem to only be able to import GIS datasourced layers, the closest of which to my needs seems to be GeoTIFF.

Answer

Use an imageOverlay layer. You only need to specify the bounding box of the image. Check the example of the API documentation:

var imageUrl = 'http://www.lib.utexas.edu/maps/historical/newark_nj_1922.jpg',
    imageBounds = [[40.712216, -74.22655], [40.773941, -74.12544]];

L.imageOverlay(imageUrl, imageBounds).addTo(map);