Vergrößern

<img src="Bild-URL" height="150" width="200" onclick="this.src='LINK';this.height=300;this.width=400" ondblclick="this.src='LINK';this.height=150;this.width=200">

Verkleinern

<img src="Bild-URL" height="300" width="225" onclick="this.src='Bild-URL';this.height=150;this.width=112" ondblclick="this.src='Bild-URL';this.height=300;this.width=225">