zurueckon = new Image();
zurueckon.src = '../pictures/buttons/zurueckh.jpg';
zurueckoff = new Image();
zurueckoff.src = '../pictures/buttons/zurueck.jpg';
schliessenon = new Image();
schliessenon.src = '../pictures/buttons/schliessenh.jpg';
schliessenoff = new Image();
schliessenoff.src = '../pictures/buttons/schliessen.jpg';
abbrechenon = new Image();
abbrechenon.src = '../pictures/buttons/abbrechenh.jpg';
abbrechenoff = new Image();
abbrechenoff.src = '../pictures/buttons/abbrechen.jpg';

function img_act(imgName) {
 imgOn = eval(imgName + 'on.src');
 document[imgName].src = imgOn;
}

function img_inact(imgName) {
 imgOff = eval(imgName + 'off.src');
 document[imgName].src = imgOff;
}