with cte1
  as (select *
            ,RowNumber-1 as RowNumberPrev
        from yourtable
       where Pic is null
      union all
      select a.RowNumber
            ,b.Pic
            ,a.Description
            ,a.RowNumberPrev-1 as RowNumberPrev
        from cte1 as a
             inner join yourtable as b
                     on b.RowNumber=a.RowNumberPrev
       where a.Pic is null
     )
    ,cte2
  as (select *
        from yourtable
       where Pic is not null
      union all
      select RowNumber
            ,Pic
            ,Description
        from cte1
       where Pic is not null
     )
select a.Pic
      ,stuff((select ' - '+b.Description
                from cte2 as b
               where b.Pic=a.Pic
               order by b.RowNumber
                 for xml path('')
             ),1,3,''
            ) as Description
  from cte2 as a
 group by a.Pic
 order by a.Pic