var slides = ["i-01.jpg", "i-02.jpg", "i-03.jpg", "i-04.jpg", "i-05.jpg", "i-06.jpg"]; 

function slideOfTheDay(){
   var d = new Date;
   var n = dayOfYear(d) % slides.length;
   document.write('<img src="http://www.danpowerphotography.com/blog/splash/' + slides[n] + '" alt="" width="948" height="579" />');
}

function dayOfYear(date) {
   var day = 0;
   day += date.getDate();
   var month = date.getMonth();
   while (month) {
      date.setDate(0);
      day += date.getDate();
      month = date.getMonth();
   }
   return day
}