Code:

       private void resizeImage(string OriginalFile, string NewFile, int NewWidth, int MaxHeight, int MaxWidth, bool OnlyResizeIfWider)
        {
            System.Drawing.Image FullsizeImage = null;
            try
            {
                FullsizeImage = Image.FromFile(OriginalFile);
            }
            catch
            {
               // error
            }
        
                if (OnlyResizeIfWider)
                {
                    if (FullsizeImage.Width <= NewWidth)
                    {
                        NewWidth = FullsizeImage.Width;
                    }
                }

                int NewHeight = FullsizeImage.Height * NewWidth / FullsizeImage.Width;
                if (NewHeight > MaxHeight)
                {
                    // Resize with height instead
                    NewWidth = FullsizeImage.Width * MaxHeight / FullsizeImage.Height;
                    NewHeight = MaxHeight;
                }

                System.Drawing.Image NewImage = FullsizeImage.GetThumbnailImage(NewWidth, NewHeight, null, IntPtr.Zero);

                // Clear handle to original file so that we can overwrite it if necessary
                FullsizeImage.Dispose();

                // Save resized picture
                try
                {

                     NewImage.Save(NewFile);
                }
                catch 
                {
                   // error
                }
        }

Code:

Stream streem = new MemoryStream();
NewImage.Save(streem);
return Image.FromStream(streem);

Code:
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        Dim slika As String = Server.MapPath(Request.QueryString("slika"))
        
        Dim objImage As System.Drawing.Image
        Dim objThumbnail As System.Drawing.Image
        Dim strServerPath, strFilename As String
        Dim shtWidth, shtHeight As Short

        objImage = objImage.FromFile(slika)
        
        if request.querystring("sirina")=nothing then
        shtwidth=objimage.Width 
        else
        shtWidth = 340
        end if


        ' Work out a proportionate height from width
        shtHeight = objImage.Height / (objImage.Width / shtWidth)
        ' Create thumbnail
        objThumbnail = objImage.GetThumbnailImage(shtWidth, _
          shtHeight, Nothing, System.IntPtr.Zero)
        ' Send down to client
        Response.ContentType = "image/jpeg"
        objThumbnail.Save(Response.OutputStream, System.Drawing.Imaging.ImageFormat.Jpeg)
        ' Tidy up

        objImage.Dispose()
        objThumbnail.Dispose()
    End Sub