Uso questo:
static public void ResizeAndSave(Stream imgStr, int Width, int Height, string FileName)
{
int imgHeight;
int imgWidth;
//creo il bitmap dallo stream
System.Drawing.Image bmpStream = System.Drawing.Image.FromStream(imgStr);
//scelta delle dimensioni delle immagini
if (bmpStream.Width > bmpStream.Height)
{
imgHeight = (Width * bmpStream.Height) / bmpStream.Width;
imgWidth = Width;
}
else
{
imgWidth = (Height * bmpStream.Width) / bmpStream.Height;
imgHeight = Height;
}
//creo un nuovo bitmap ridimensionandolo
Bitmap img = new Bitmap(bmpStream, new Size(imgWidth, imgHeight));
//salvo l'immagine ridimensionata
img.Save(FileName, System.Drawing.Imaging.ImageFormat.Jpeg);
}
Se vuoi il crop: