Ottima idea... Solo non trovo il comando per settare size min e size max! Saresti così gentile da suggerirmeli? Ti passo anche il code (molto semplice) della mia pagina. Grazie mille.
codice:
<%@ Page Language="C#" %>
<%@ import Namespace="System.Drawing" %>
<%@ import Namespace="System.Drawing.Imaging" %>
<%@ import Namespace="System.Text.RegularExpressions" %>
<script runat="server">

    System.Drawing.Image oldImage, newImage;

    void Page_Load(Object sender, EventArgs e) {
        if ( Request.QueryString["FileName"] != null ) {
            string strFileName = Convert.ToString(Request.QueryString["FileName"]);
            if ( strFileName != "" ) {
                try {
                    oldImage = System.Drawing.Image.FromFile( Server.MapPath("public/minisito/"+Request.QueryString["id"]+"/"+strFileName) );

			if ( oldImage.Width > oldImage.Height ) {
                        newImage = oldImage.GetThumbnailImage( 120, 90, null, IntPtr.Zero);
			} else {
			newImage = oldImage.GetThumbnailImage( 90, 120, null, IntPtr.Zero);
			}
                        Response.ContentType = "image/jpeg";
                        newImage.Save(Response.OutputStream, System.Drawing.Imaging.ImageFormat.Jpeg);
                        oldImage.Dispose();
                        newImage.Dispose();
                        oldImage = null;
                        newImage = null;
                  
                } catch (Exception ex) {
                    Response.Write(ex.Message);
                }
            }
        }
    }

</script>