Use the Image property to assign an icon or a picture to the group. Use the ImageAlignment property to align the image inside the group's header. Use the Images and ReplaceIcon methods to update the images list collection, at runtime. Use the HTMLPicture property to add custom-sized pictures to your caption.

The following sample adds a group that displays a custom size picture using BASE 64 encoding:

With ExplorerTree1.Groups
    With .Add("new")
        Dim s As String
        s = "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"
        s = s + "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"
        .Image = s
    End With
End With