if (document.images) {
     button1 = new Image
     button2 = new Image
     button3 = new Image
     button4 = new Image
     button5 = new Image
     button6 = new Image
     button7 = new Image
     button8 = new Image
     button9 = new Image
     button10 = new Image
     button11 = new Image
     button12 = new Image

     button1.src = 'images/photo_button_on.png'
     button2.src = 'images/photo_button.png'
     button3.src = 'images/headlines_button_on.png'
     button4.src = 'images/headlines_button.png'
     button5.src = 'images/links_button_on.png'
     button6.src = 'images/links_button.png'
     button7.src = 'images/contact_button_on.png'
     button8.src = 'images/contact_button.png'
     button9.src = 'images/media_on.png'
     button10.src = 'images/media_off.png'
     button11.src = 'images/events_on.png'
     button12.src = 'images/events_off.png'
 }