function changeDivImagea() 

{ 

    document.getElementById("display").style.background = "url(./portfolio/hea1a.jpg)"; 

} 

function changeDivImageb() 

{ 

    document.getElementById("display").style.background = "url(./portfolio/hea1b.jpg)"; 

} 

function changeDivImagec() 

{ 

    document.getElementById("display").style.background = "url(./portfolio/hea1c.jpg)"; 

} 
function changeDivImaged() 

{ 

    document.getElementById("display").style.background = "url(./portfolio/hea1d.jpg)"; 

}