How Do I Create Thumbnails?

I'd create a subdirectory called "Thumbs" and store the thumb image in that under exactly the same name as the full image.
Then I use this code:

/// <summary>
/// Create a thumbnail image.
/// </summary>
/// <param name="path">path to full size image</param>
/// <param name="width">Width of thumbnail</param>
/// <param name="height">Height of thumbnail</param>
public static Image GetThumbnailImage(string path, int width, int height)
    {
    using (Image image = Image.FromFile(path))
        {
        Image.GetThumbnailImageAbort myCallback = new Image.GetThumbnailImageAbort(ThumbnailCallback);
        return image.GetThumbnailImage(width, height, myCallback, IntPtr.Zero);
        }
    }
/// <summary>
/// This is not used in GDI+ 1.0, but must be supplied to some GDI calls.
/// E.g. Image.GetThumbnailImage
/// </summary>
/// <returns>false always</returns>
private static bool ThumbnailCallback()
    {
    return false;
    }

All you need then is to call Image.Save to save the thumbnail.