How to give preview option and back option in asp.net using vb.net or c#.net

Hi ,Can please tell how to solve my problem regarding giving preview option and back button, My task is uploading image in server, I am uploading one image using upload file control  in asp.net and I wrote code for uploading image in server its is working fine, After uploading image I am giving an option to see preview in other page and I am giving back button, up to here it is working fine My problem is after click back he will once again come back to uploading image page, if once again if he want to see preview , after click preview button I am getting error, because in uploading control no image path, if we give  same image path it will over write so I donââ?¬â?¢t want to over write imageif&nb ...