you can use the following codes to achieve image resizing
efficiently.i used it in my application.

String upName = null;
const int bmpH = 100;
const int bmpW = 125;

Int32 newWidth = bmpW;
Int32 newHeight = bmpH;
string filePath = "";

// any path where the file will be saved
filePath = Server.MapPath(subPath + "\\" + User_Name) + "\\" + ImageName; //main image path to be saved

Bitmap upBmp = (Bitmap)Bitmap.FromStream(fileUpload.PostedFile.InputStream);
Double upWidth = upBmp.Width;
Double upHeight = upBmp.Height;
Double reDuce = 0;
if (upWidth > upHeight)
{
//Landscape picture
reDuce = newWidth / upWidth;
newHeight = ((Int32)(upHeight * reDuce));

}
else if (upWidth < upHeight)
{
//Portrait picture
reDuce = newHeight / upHeight;
newWidth = ((Int32)(upWidth * reDuce));
}

else if (upWidth == upHeight)
{
//square picture
reDuce = newHeight / upHeight;
newWidth = ((Int32)(upWidth * reDuce));

}
Bitmap newBmp = new Bitmap(newWidth, newHeight, System.Drawing.Imaging.PixelFormat.Format24bppRgb);//new
newBmp.SetResolution(96, 96);
Graphics newGraphic = Graphics.FromImage(newBmp);
try
{
newGraphic.Clear(Color.White);
newGraphic.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.AntiAlias;
newGraphic.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
newGraphic.CompositingQuality = CompositingQuality.HighQuality;//new
newGraphic.DrawImage(upBmp, 0, 0, newWidth, newHeight);
newBmp.Save(filePath, System.Drawing.Imaging.ImageFormat.Jpeg);
}
catch { }
finally { upBmp.Dispose(); newBmp.Dispose(); newGraphic.Dispose(); }

good luck........