Create image thumbnail

using System;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.IO;
using System.Net;

namespace Thumbnailer
{
    public static class Thumbnail
    {
        /// <summary>
        ///
        /// </summary>
        /// <param name="source">The image to crop</param>
        /// <param name="dimension">The maximum size of the resulting image</param>
        /// <returns></returns>
        private static Image Crop(Image source, int dimension)
        {
            Image resizedSource = Resize(source, dimension);

            int diffX = (resizedSource.Width - dimension);
            int diffY = (resizedSource.Height - dimension);

            int x = diffX > 1 ? diffX / 2 : 0;
            int y = diffY > 1 ? diffY / 2 : 0;

            var cropRectangle = new Rectangle(x, y, dimension, dimension);
            var sourceImage = new Bitmap(resizedSource);
            Bitmap croppedImage = sourceImage.Clone(cropRectangle, sourceImage.PixelFormat);

            return croppedImage;
        }

        /// <summary>
        ///
        /// </summary>
        /// <param name="path">The full path of the image to download</param>
        /// <param name="dimension">The maximum size of the resulting image</param>
        /// <param name="maintainAspect">Determines if the resulting image should maintain its original aspect ratio</param>
        /// <returns></returns>
        public static Image Generate(string path, int dimension, bool maintainAspect)
        {
            if (File.Exists(path))
            {
                Image image = Image.FromFile(path);
                return maintainAspect ? Resize(image, dimension) : Crop(image, dimension);
            }

            return null;
        }

        /// <summary>
        ///
        /// </summary>
        /// <param name="url">The URL of the image to download</param>
        /// <param name="dimension">The maximum size of the resulting image</param>
        /// <param name="maintainAspect">Determines if the resulting image should maintain its original aspect ratio</param>
        /// <returns></returns>
        public static Image Generate(Uri url, int dimension, bool maintainAspect)
        {
            var request = (HttpWebRequest)WebRequest.Create(url);
            request.AllowWriteStreamBuffering = true;
            request.UserAgent = "Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1)";
            request.Referer = "http://www.google.com/";
            request.Timeout = 30000;

            WebResponse response = request.GetResponse();
            Stream stream = response.GetResponseStream();

            if (stream != null)
            {
                Image image = Image.FromStream(stream);
                response.Close();

                return maintainAspect ? Resize(image, dimension) : Crop(image, dimension);
            }

            return null;
        }

        /// <summary>
        ///
        /// </summary>
        /// <param name="source">The image to resize</param>
        /// <param name="dimension">The maximum size of the resulting image</param>
        /// <returns></returns>
        private static Image Resize(Image source, int dimension)
        {
            float factor;

            if (source.Height <= source.Width)
                factor = (dimension + 1) / (float)source.Height;
            else
                factor = (dimension + 1) / (float)source.Width;

            var destWidth = (int)(source.Width * factor);
            var destHeight = (int)(source.Height * factor);

            var bmp = new Bitmap(destWidth, destHeight);
            Graphics gfx = Graphics.FromImage(bmp);

            gfx.InterpolationMode = InterpolationMode.HighQualityBicubic;
            gfx.DrawImage(source, 0, 0, destWidth, destHeight);
            gfx.Dispose();

            return bmp;
        }
    }
}