Add an icon to the map
Add an icon to the map from an external URL and use it in a symbol layer.
<!DOCTYPE html>
<html>
<head>
    <meta charset='utf-8' />
    <title></title>
    <meta name='viewport' content='initial-scale=1,maximum-scale=1,user-scalable=no' />
    <script src='https://api.tiles.mapbox.com/mapbox-gl-js/v0.36.0/mapbox-gl.js'></script>
    <link href='https://api.tiles.mapbox.com/mapbox-gl-js/v0.36.0/mapbox-gl.css' rel='stylesheet' />
    <style>
        body { margin:0; padding:0; }
        #map { position:absolute; top:0; bottom:0; width:100%; }
    </style>
</head>
<body>

<div id='map'></div>

<script>
mapboxgl.accessToken = '<your access token here>';

var map = new mapboxgl.Map({
    container: 'map',
    style: 'mapbox://styles/mapbox/streets-v9'
});

map.on('load', () => {
    map.loadImage('https://upload.wikimedia.org/wikipedia/commons/thumb/6/60/Cat_silhouette.svg/400px-Cat_silhouette.svg.png', (error, image) => {
        if (error) throw error;
        map.addImage('cat', image);
        map.addLayer({
            "id": "points",
            "type": "symbol",
            "source": {
                "type": "geojson",
                "data": {
                    "type": "FeatureCollection",
                    "features": [{
                        "type": "Feature",
                        "geometry": {
                            "type": "Point",
                            "coordinates": [0, 0]
                        }
                    }]
                }
            },
            "layout": {
                "icon-image": "cat",
                "icon-size": 0.25
            }
        });
    });
});

</script>

</body>
</html>
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