div.swapimage {
  width: 220px;
  height: 220px;
}

div.swapimage span {
  display: block;
  width: 220px;
  height: 220px;
  background-image: url(/foswiki/pub/Allgemeines/FolkmarBornemann/Bornemann_07_07.jpg);
}

div.swapimage span:hover {
  background-image: url(/foswiki/pub/Allgemeines/FolkmarBornemann/Bornemann_11_06a.jpg);
}