You'll need Javascript or another client side language. As PHP is Server-side, it can only handle things on the server.
With Javascript you could create an image place holder and change its source dyanamically when a preview button is pressed.
For specifics go to the JS forum here:forum216
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Ignorance is not necessarily Bliss, case in point:
Unknown has caused an Unknown Error on Unknown and must be shutdown to prevent damage to Unknown.