Incase it is of any use, here is the code I use to resize and save the image:
Dim aFile As HttpPostedFile = Me.myFile.PostedFile
Dim fileName As String = Path.GetFileName(aFile.FileName)
Dim imgStream As Stream = aFile.InputStream()
Dim img_New As System.Drawing.Image = System.Drawing.Image.FromStream(imgStream)
Dim imgOutput As New System.Drawing.Bitmap(img_New,800,600)
imgOutput.Save(Server.MapPath(".") & fileName)
As I said, using this method seems to increase the file size.
Any help is appreciated.