Quite an annoying aspect of WordPress is that its not very easy to use an image rollover from within posts. This is a simple hack that lets you use an image rollover in WordPress without the use of a plugin.

<img title="this" onmouseover="this.src='http://twentyeleven.co.uk/wp-content/uploads/2012/05/that.png';" onmouseout="this.src='http://twentyeleven.co.uk/wp-content/uploads/2012/05/this.png';" src="http://twentyeleven.co.uk/wp-content/uploads/2012/05/this.png" alt="" width="192" height="116" />