Image img = Image.FromFile("is_smile.png");
Clipboard.Clear();
Clipboard.SetImage(img);
richTextBox1.Paste();
Clipboard.Clear();

Image img = Image.FromFile(@"is_smile.png");
Clipboard.SetDataObject(img);
DataFormats.Format dataFormat =
DataFormats.GetFormat(DataFormats.Bitmap);
if (richTextBox1.CanPaste(dataFormat))
{
    richTextBox1.Paste(dataFormat);
}

Bitmap myBitmap = new Bitmap(Properties.Resources.is_smile);
Clipboard.SetDataObject(myBitmap);
DataFormats.Format myFormat = DataFormats.GetFormat(DataFormats.Bitmap);
richTextBox1.Paste(myFormat);

Hashtable emotions;

void CreateEmotions()
{
    emotions = new Hashtable(2);
    emotions.Add(":-)", Properties.Resources.is_smile);
    emotions.Add(":)", Properties.Resources.is_smile);
}

void AddEmotions()
{
    foreach (string emote in emotions.Keys)
    {
        while (richTextBox1.Text.Contains(emote))
        {
            int ind = richTextBox1.Text.IndexOf(emote);
            richTextBox1.Select(ind, emote.Length);
            Clipboard.SetImage((Image)emotions[emote]);
            richTextBox1.Paste();
        }
    }
}

private void richTextBox1_TextChanged_1(object sender, EventArgs e)
{
    AddEmotions();
}