SilverStripe 4.0 or higher SS3-4 upgrade: moved LatLongField::google_maps_api_key to environment var (see Config below)
.env:
GMAPS_API_KEY="..."
GMAPS_BROWSER_KEY="..." (optional secondary 'public' key to use in the browser)
<img src="//maps.googleapis.com/maps/api/staticmap?center=Leiden+NL&size=600x600&key=$GMapsApiKey" />