ToolStripItem.BackgroundImageLayout Property

// This utility method creates a RolloverItem  
// and adds it to a ToolStrip control. 
private RolloverItem CreateRolloverItem(
    ToolStrip owningToolStrip,
    string txt,
    Font f,
    string imgKey,
    TextImageRelation tir,
    string backImgKey)
{
    RolloverItem item = new RolloverItem();

    item.Alignment = ToolStripItemAlignment.Left;
    item.AllowDrop = false;
    item.AutoSize = true;

    item.BackgroundImage = owningToolStrip.ImageList.Images[backImgKey];
    item.BackgroundImageLayout = ImageLayout.Center;
    item.DisplayStyle = ToolStripItemDisplayStyle.ImageAndText;
    item.DoubleClickEnabled = true;
    item.Enabled = true;
    item.Font = f;

    // These assignments are equivalent. Each assigns an 
    // image from the owning toolstrip's image list.
    item.ImageKey = imgKey;
    //item.Image = owningToolStrip.ImageList.Images[infoIconKey]; 
    //item.ImageIndex = owningToolStrip.ImageList.Images.IndexOfKey(infoIconKey);
    item.ImageScaling = ToolStripItemImageScaling.None;

    item.Owner = owningToolStrip;
    item.Padding = new Padding(2);
    item.Text = txt;
    item.TextAlign = ContentAlignment.MiddleLeft;
    item.TextDirection = ToolStripTextDirection.Horizontal;
    item.TextImageRelation = tir;

    return item;
}