方式一：

 /// <summary>
        /// 从程序集中加载图片
        /// </summary>
        /// <param name="imagePathName">图片路径（该图片必须是嵌入的资源）</param>
        /// <returns>Bitmap 格式图片</returns>
        public Bitmap GetIcon(string imagePathName)
        {
            Bitmap b = null;
            try
            {
                Assembly asm1 = Assembly.GetExecutingAssembly();
                string name = asm1.GetName().Name;
                asm1.GetManifestResourceStream(imagePathName);
                Stream imageStream = asm1.GetManifestResourceStream(imagePathName);
                if (imageStream != null)
                {
                    b = new Bitmap(Image.FromStream(imageStream));
                    b.MakeTransparent();
                }
            }
            catch (Exception e)
            {
                throw new Exception(e.Message);
            }
            return b;
        }

方式二、

 /// <summary>
        /// 根据图片路径加载图片
        /// </summary>
        /// <param name="imagePathName">图片路径</param>
        /// <returns>Bitmap格式图片</returns>
        public Bitmap GetToolIcon(string imagePathName)
        {
            Bitmap b = null;
            if (!File.Exists(imagePathName))
            {
                MessageBox.Show("该路径下：" + imagePathName.ToString() + "!文件找不到");
                return b;
            }
            try
            {
                FileStream fs = new FileStream(imagePathName, FileMode.Open, FileAccess.Read);
                b = (Bitmap)System.Drawing.Bitmap.FromStream(fs);
            }
            catch (Exception e)
            {
                throw new Exception(e.Message);
            }
            return b;
        }

WinForm 加载本地图片