When your image will be uploaded then at that time call a image binding method or write a code for binging that particular image with your control
string path = "~/Images/" + FileUpload1.FileName;
Image1.ImageUrl = path;
Image1.DataBind();
here i have uploaded all my images in to Images derictory so i used "~/Images/"
you can use your path insted this and get the uploaded file name using FileUpload controls FileName property for binding current image to your image viewer control...