Why do "deleted" photos stick around so long? The problem relates to the way data is stored on large websites: While your personal computer only keeps one copy of a file, large-scale services like Facebook rely on what are called content delivery networks to manage data and distribution. It's a complex system wherein data is copied to multiple intermediate devices, usually to speed up access to files when millions of people are trying to access the service at the same time. But because changes aren't reflected across the content delivery networks immediately, ghost copies of files tend to linger for days or weeks. 　　In the case of Facebook, the company says data may hang around until the URL in question is reused, which is usually "after a short period of time", though obviously that time can vary considerably.