Hi use a librariy that help you to view images from URL. visit https://github.com/nostra13/Android-Universal-Image-Loader for Android-Universal-Image-Loader
also you can visit to know for downloading the image
http://brainflush.wordpress.com/2009/11/23/droid-fu-part-2-webimageview-and-webgalleryadapter/
and after that
for the Custom Marker Icon, you can use an icon to show as a marker. load the icon from any kind of supported sources.
fromAsset(String assetName) – Loading from assets folder
fromBitmap (Bitmap image) – Loading bitmap image
fromFile (String path) – Loading from file
fromResource (int resourceId) – Loading from drawable resource
try as follows
// latitude and longitude
double latitude = 17.385044;
double longitude = 78.486671;
// create marker
MarkerOptions marker = new MarkerOptions().position(new LatLng(latitude, longitude)).title("Hello Maps");
// Changing marker icon
// set yours icon here
marker.icon(BitmapDescriptorFactory.fromResource(R.drawable.my_marker_icon)));
// adding marker
googleMap.addMarker(marker);