How to add image for button in android?

Simply use ImageButton View and set image for it:`

 <ImageButton
    android:id="@+id/searchImageButton"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentTop="true"
    android:layout_alignParentRight="true"
    android:src="@android:drawable/ic_menu_search" />

You should try something like this

    <Button
    android:id="@+id/imageButton1"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:background="@drawable/qrcode"/>

the android:background="@drawable/qrcode" will do it

As he stated, used the ImageButton widget. Copy your image file within the Res/drawable/ directory of your project. While in XML simply go into the graphic representation (for simplicity) of your XML file and click on your ImageButton widget that you added, go to its properties sheet and click on the [...] in the src: field. Simply navigate to your image file. Also, make sure you're using a proper format; I tend to stick with .png files for my own reasons, but they work.

Rather humorously, considering your tags, just use the ImageButton widget.