How to set the button background image through code

I am using a Button created using following code

LinearLayout ll = new LinearLayout(this);
ll.setOrientation(LinearLayout.VERTICAL);

Button btn = new Button(this);
btn.setOnClickListener(newtodobtn);
btn.setText("New Todo");

btn.setBackgroundDrawable(new Button(this).getBackground());

ll.addView(btn);

I have an image in path @drawable/new_todo_image to set as background for the button. How to set it to the Button programmatically?