function random_image() 
{ 
image_array = new Array(); 
image_array[0] = '../images/top_images/top_image_a.jpg'; 
image_array[1] = '../images/top_images/top_image_b.jpg'; 
image_array[2] = '../images/top_images/top_image_c.jpg';
image_array[3] = '../images/top_images/top_image_d.jpg';
image_array[4] = '../images/top_images/top_image_e.jpg';
image_array[5] = '../images/top_images/top_image_f.jpg';
image_array[6] = '../images/top_images/top_image_g.jpg';   

count = image_array.length; 
random = Math.floor(Math.random() * count); 

document.getElementById('bgChange').style.backgroundImage = "url(" + image_array[random] + ")"; 
}