Android : Map Marker bitmap based drawing

In the Google Maps API v2 Demo there is a MarkerDemoActivity class in which you can see how a custom Image is set to a GoogleMap.

// Uses a custom icon.
mSydney = mMap.addMarker(new MarkerOptions()
    .position(SYDNEY)
    .title("Sydney")
    .snippet("Population: 4,627,300")
    .icon(BitmapDescriptorFactory.fromResource(R.drawable.arrow)));
As this just replaces the marker with an image you might want to use a Canvas to draw more complex and fancier stuff:

Bitmap.Config conf = Bitmap.Config.ARGB_8888;
Bitmap bmp = Bitmap.createBitmap(80, 80, conf);
Canvas canvas1 = new Canvas(bmp);

// paint defines the text color, stroke width and size
Paint color = new Paint();
color.setTextSize(35);
color.setColor(Color.BLACK);

// modify canvas
canvas1.drawBitmap(BitmapFactory.decodeResource(getResources(),
    R.drawable.user_picture_image), 0,0, color);
canvas1.drawText("User Name!", 30, 40, color);

// add marker to Map
mMap.addMarker(new MarkerOptions()
    .position(USER_POSITION)
    .icon(BitmapDescriptorFactory.fromBitmap(bmp))
    // Specifies the anchor to be at a particular point in the marker image.
    .anchor(0.5f, 1));
This draws the Canvas canvas1 onto the GoogleMap mMap. The code should (mostly) speak for itself, there are many tutorials out there how to draw a Canvas. You can start by looking at the Canvas and Drawables from the Android Developer page.

Now you also want to download a picture from an URL.

URL url = new URL(user_image_url);
HttpURLConnection conn = (HttpURLConnection) url.openConnection(); 
conn.setDoInput(true); 
conn.connect();   
InputStream is = conn.getInputStream();
bmImg = BitmapFactory.decodeStream(is);
You must download the image from an background thread (you could use AsyncTask or Volley or RxJava for that).

After that you can replace the BitmapFactory.decodeResource(getResources(), R.drawable.user_picture_image) with your downloaded image bmImg.

references:
https://stackoverflow.com/questions/14811579/how-to-create-a-custom-shaped-bitmap-marker-with-android-map-api-v2