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();
              }
        }

转载于:https://www.cnblogs.com/hzuIT/articles/819100.html