try this
System.Web.UI.WebControls.Image objImage = Page.ResolveUrl("~/") + "ImageGenerator.aspx?path=" + Server.MapPath(picturefilename.ToString());
now in ImageGenerator.aspx.cs
protected void Page_Load(object sender, EventArgs e)
{
string fileName = Request.QueryString["path"];
System.Drawing.Image resizedImage = System.Drawing.Image.FromFile(fileName);
// make a memory stream to work with the image bytes
MemoryStream imageStream = new MemoryStream();
// put the image into the memory stream
resizedImage.Save(imageStream, System.Drawing.Imaging.ImageFormat.Jpeg);
// make byte array the same size as the image
byte[] imageContent = new Byte[imageStream.Length];
// rewind the memory stream
imageStream.Position = 0;
// load the byte array with the image
imageStream.Read(imageContent, 0, (int)imageStream.Length);
// return byte array to caller with image type
Response.ContentType = "image/jpeg";
Response.BinaryWrite(imageContent);
}