richTextBox支持图片格式，插入图片的方法如下：

 private void button2_Click(object sender, EventArgs e)
        {
              openFileDialog1.Filter   =   "图片文件|*.jpg|所有文件|*.*";   
              if(openFileDialog1.ShowDialog()   ==   DialogResult.OK)   
              {   
                 Clipboard.SetDataObject(Image.FromFile(openFileDialog1.FileName),false);   
                 richTextBox1.Paste();   
              }       
        }