Here you will need to put some logic to capture which bitmap Image was clicked.
One technique which works in my case is to override a method in your ItemizedOverlay class
protected boolean onTap(int index) {
// Here you get the index of which bitmap image was tapped on
// You can map this index to the related activity you need to open by mean of your logic
OverlayItem item = mOverlays.get(index);
Intent intent=new Intent (context,YourActivity.class);
context.startActivity(intent);
return true;
}