var parta='<br><img src=" '
var partc='.jpg" >'

function get_randompix2()
{
    var ranpix_number=Math.floor(Math.random()*5); 

    return ranpix_number;
}

var partb=get_randompix2();

var iframecode=parta+partb+partc

document.write(iframecode)