Downloads/transforms images with Glide and puts them on Google Map as markers (images will be cached automatically).

DownloadTransformImagesAndPutThemAsMarkersOnMapWithGlide.java

private Bitmap defaultPin;
private GoogleMap googleMap;
private List<MapItem> items;

private void putItemsOnMap() {
    for (MapItem item : items) {
        // wrap google map marker with target, also set marker's pin with default pin bitmap, coordinates, etc, so it still be shown on map while real one is downloaded/transformed
        MarkerTarget marker = new MarkerTarget(googleMap.addMarker(new MarkerOptions().position(new LatLng(item.getLatitude(), item.getLongitude())).title(item.getName()).icon(BitmapDescriptorFactory.fromBitmap(defaultPin))));
        Glide.with(this)
                .load(item.getPinImageUrl())
                .asBitmap()
                .transform(new OverlayTransformation(getContext(), defaultPin))
                .into(marker)
    }
}

class MapItem {
    
    private String pinImageUrl;
    private double latitude;
    private double longitude;
    private String name;
    
    public getPinImageUrl() {
        return pinImageUrl;
    }
    
    public getLatitude() {
        return latitude;
    }
    
    public getLongitude() {
        return longitude;
    }
    
    public getName() {
        return name;
    }
    
}
    
class MarkerTarget extends SimpleTarget<Bitmap> {

    private Marker marker;

    public MarkerTarget(Marker marker) {
        this.marker = marker;
    }

    @Override
    public void onResourceReady(Bitmap resource, GlideAnimation<? super Bitmap> glideAnimation) {
        marker.setIcon(BitmapDescriptorFactory.fromBitmap(resource));
    }

}

class OverlayTransformation extends BitmapTransformation {

    private Bitmap bitmapToOverlayOn;

    public OverlayTransformation(Context context, Bitmap bitmapToOverlayOn) {
        super(context);
        this.bitmapToOverlayOn = bitmapToOverlayOn;
    }

    @Override
    protected Bitmap transform(BitmapPool pool, Bitmap toTransform, int outWidth, int outHeight) {
        Bitmap transformed = Bitmap.createBitmap(bitmapToOverlayOn.getWidth(), bitmapToOverlayOn.getHeight(), bitmapToOverlayOn.getConfig());
        Canvas canvas = new Canvas(transformed);
        canvas.drawBitmap(bitmapToOverlayOn, new Matrix(), null);
        canvas.drawBitmap(toTransform, (bitmapToOverlayOn.getWidth() - toTransform.getWidth()) / 2,
                    (bitmapToOverlayOn.getHeight() - toTransform.getHeight()) / 2, null);
        return transformed;
    }

    @Override
    public String getId() {
        return "OverlayTransformation";
    }
    
}