UPDATED

<!DOCTYPE html>
<html>
<head>
<meta charset=utf-8 />
<title>Leaflet Image</title>

<button id='snap' style='position: absolute; bottom: 10px; right: 10px;'>Snap image</button>
    <div id='images' style='float: right; width: 49%;'></div>
    <div id='map' style='width: 49%;'></div>

document.getElementById('snap').addEventListener('click', function() {
            leafletImage(map, doImage);
        });

function doImage(err, canvas) {
            var img = document.createElement('img');
            
            img.width = 800;
            img.height = 400;
            img.src = canvas.toDataURL();
            document.getElementById('images').innerHTML = '';
            document.getElementById('images').appendChild(img);
        }
    </script>

</body>
</html>

https://api.tiles.mapbox.com/mapbox.js/v1.6.1/mapbox.js

https://api.tiles.mapbox.com/mapbox.js/plugins/leaflet-image/v0.0.3/leaflet-image.js