After explaining how to create buttons with a built-in Office picture using the CommandBarButton.FaceId property, the next step is to use custom pictures. Tricky as always for the conversion from .NET bitmap to OLE IPictureDisp, but at least fortunately the use of the clipboard (CommandBarButton.PasteFace) is no longer necessary as it was in initial versions of Microsoft Office and in VB5/VB6 add-ins.
HOWTO: Create a button with a custom picture for the VBA editor of Office from an add-in with Visual Studio .NET.
http://www.mztools.com/articles/2012/MZ2012016.aspx