If the Variable is False, that doesn't means that the Property object contains a real property. Use the PropertyPage property to determine if the Property object contains a properties page, or use the Category to check whether the Property object contains a category. Use the ShowVariables property to exclude variables.  Use the Variable property to filter your items like in the following sample:

Private Sub PropertiesList1_IncludeProperty(ByVal Property As EXPROPERTIESLISTLibCtl.IProperty, Cancel As Boolean)
    If Not (Property.Object Is Nothing) Then
        Cancel = Property.Variable And TypeOf Property.Object Is IPictureDisp
    End If
End Sub