function CheckBox(feld){
 if(document.form[feld].value == 'true'){
   document.form[feld].value = 'false';
   document.images[feld].src = 'res/images/icons/checkbox.png';
 }
 else{
   document.form[feld].value = 'true';
   document.images[feld].src = 'res/images/icons/checkboxActive.png';
 }
}