var img, img2,img3, img4, i = 2, interval; 

window.onload = function()
{
  img = document.getElementById('animace').getElementsByTagName('img')[1];
  img2 = document.getElementById('animace').getElementsByTagName('img')[0];  
  img3 = document.getElementById('animace').getElementsByTagName('img')[2];
  img4 = document.getElementById('animace').getElementsByTagName('img')[3];  
  
  interval = window.setInterval("animation()", 5000);
}

function change_picture(id)
{
  window.clearInterval(interval);
  img2.src = "pics_system/uvodni-stranka/photo" + (id) + ".jpg";
  i = id;
  interval = window.setInterval("animation()", 5000);
  new Effect.Opacity(img, {duration: 1.5, from: 1.0, to: 0.0, afterFinish: change_pictures});
}

function animation()
{
  new Effect.Opacity(img, {duration: 1.5, from: 1.0, to: 0.0, afterFinish: change_pictures});       
}

function change_pictures()
{
  img.src = img2.src;
  img.style.opacity = 1.0;
  img.style.filter = "alpha(opacity=100)";    
  img3.src = img3.src.replace(/_hover/, '')
  
  img3 = document.getElementById('animace').getElementsByTagName('img')[i+1];  
  img3.src = "pics_system/uvodni-stranka/" + (i) + "_hover.png";  

  i++;

  if(i > 3)
    i = 1;

  img2.src = "pics_system/uvodni-stranka/photo" + i + ".jpg";
}