I believe that you need something that resizes, maintaining the aspect ratio, like in this snippet:

C#: Resize An Image While Maintaining Aspect Ratio and Maximum Height
http://snippets.dzone.com/posts/show/4336

C#:

public void ResizeImage(string OriginalFile, string NewFile, int NewWidth, int MaxHeight, bool OnlyResizeIfWider)
{
	System.Drawing.Image FullsizeImage = System.Drawing.Image.FromFile(OriginalFile);

	// Prevent using images internal thumbnail
	FullsizeImage.RotateFlip(System.Drawing.RotateFlipType.Rotate180FlipNone);
	FullsizeImage.RotateFlip(System.Drawing.RotateFlipType.Rotate180FlipNone);

	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
	NewImage.Save(NewFile);
}

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VB.NET:

Public Sub ResizeImage(OriginalFile As String, NewFile As String, NewWidth As Integer, MaxHeight As Integer, OnlyResizeIfWider As Boolean)
	Dim FullsizeImage As System.Drawing.Image = System.Drawing.Image.FromFile(OriginalFile)

	' Prevent using images internal thumbnail
	FullsizeImage.RotateFlip(System.Drawing.RotateFlipType.Rotate180FlipNone)
	FullsizeImage.RotateFlip(System.Drawing.RotateFlipType.Rotate180FlipNone)

	If OnlyResizeIfWider Then
		If FullsizeImage.Width <= NewWidth Then
			NewWidth = FullsizeImage.Width
		End If
	End If

	Dim NewHeight As Integer = FullsizeImage.Height * NewWidth \ FullsizeImage.Width
	If NewHeight > MaxHeight Then
		' Resize with height instead
		NewWidth = FullsizeImage.Width * MaxHeight \ FullsizeImage.Height
		NewHeight = MaxHeight
	End If

	Dim NewImage As System.Drawing.Image = FullsizeImage.GetThumbnailImage(NewWidth, NewHeight, Nothing, IntPtr.Zero)

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

	' Save resized picture
	NewImage.Save(NewFile)
End Sub

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This looks like it will work. There are a few things I do not understand.
Why is the image Rotated twice? The first two lines of code.

You use the GetThumbnail method to resize the image. But if a thumbnail exists it scales the thumbnail and not the original image. I am concerned about the quality of a scaled thumbnail. Your comments suggest that by rotating the image, the thumbnail will not be used. But I do not understand.

Lastly, I am used to Photoshop where I always specify a Interpolation method when resizing either up or down. I found the same property in MSDN but I do not see how to apply it in your code. Could you please help?
http://msdn.microsoft.com/en-us/library/system.drawing.drawing2d.interpolationmode.aspx

thanks,
pat

check this sample

http://www.devasp.net/net/articles/display/1095.html

Thank you