managing image files with PHP/Mysql

Hello, I want to thank Kathleen and other people for ideas about uploading / displaying images using PHP and Mysql. I checked these ideas and they work very well, so I will use them into my program. For storing and retrieving image streams, I used addslashes and stripslashes PHP functions. The only problem still remaining is on client-side point of view. When somebody going to upload file, browsers open little box to let user choose file (<input type="FILE"...>). I wish user to know somewhat is the image he/she is going to upload, so I want to display this image before user uploading. For this action, I would be able to control the 'BROWSE' button that appears on form. Since this button doesn't apply to POST method, nor it will execute function on Form command, how can I control this action? Is there some doc explaining features of these objects? Thanks Miguel