var n = 2;

var captions = new Array();
captions[0] = 'Philip Thornton, Partner';
captions[1] = 'Ruth Alexander, Associate';

var rand = Math.floor(Math.random()*n)+1; 
var image = 'img/random_family/' + rand + '/mainimage.jpg'
var imageElem = 'MainImage';
var captionElem = 'MainImageCaption';

//var image = 'img/estate_agents_rnd/2.jpg';
//var caption = 'Dianne Paterson, Partner';

document.getElementById(imageElem).src = image;
document.getElementById(captionElem).innerHTML=captions[rand-1];
//document.getElementById(captionElem).innerHTML=caption + ' (' + image + ')';