Assigning the menu side-bar is done through the code by setting the PopUpSideBar property of your item to desired side-bar structure.

Follow these steps to create image side-bar for an popup menu:

1. Create your menu as usual using DotNetBar designer or code
2. In the form that is hosting DotNetBarManager add new Form.Load event handler
3. Get the reference to the item that is parent of your popup menu
4. Assign to the PopUpSideBar property new instance of the SideBarImage structure that describes your side-bar

Following code is taken from Popup sample that shows how to assign the side-bar image to an popup menu:

      VB
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        ' Setup side-bar, make sure that image that is used fits, or exceeds the height
        ' Side-bar will be displayed only for popup menus
        Dim si As DevComponents.DotNetBar.SideBarImage
        si = New DevComponents.DotNetBar.SideBarImage()
        si.Picture = New Bitmap(Me.GetType(), "devco.jpg")
        ' If image exceeds the size of the popup menu this specifies the image alignment
        si.Alignment = DevComponents.DotNetBar.eAlignment.Bottom
        ' If there is no image specified gradient can be used
        si.GradientColor1 = Color.Orange
        si.GradientColor2 = Color.Black
        myParentPopupItem.PopUpSideBar = si
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      C#
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      // Setup side-bar, make sure that image that is used fits, or exceeds the height
      // Side-bar will be displayed only for popup menus
      DevComponents.DotNetBar.SideBarImage si=new DevComponents.DotNetBar.SideBarImage();
      si.Picture=new Bitmap(typeof(Popup.Form1),"devco.jpg");
      // If image exceeds the size of the popup menu this specifies the image alignment
      si.Alignment=DevComponents.DotNetBar.eAlignment.Bottom;
      // If there is no image specified gradient can be used
      si.GradientColor1=Color.Orange;
      si.GradientColor2=Color.Black;
      myParentPopupItem.PopUpSideBar=si;
      

You can find working example of menu side-bar and associated code in Popup sample.