[Solved]SharePoint 2007 error: the file is checked out or locked for editing domain\User

On my SharePoint 2007 site, I have a picture library. There was a file which I wanted to delete , but when I tried to delete it  from the library , it gave me an error “file is checked out or locked for editing by domain\user” . Actually that file was checked by a user who is no more in AD. After lot of Google search I found that , we can delete the file forcefully using SHarePoint designer.