Deleted Facebook photos don't disappear but can still be accessed by anyone with a link to the images themselves.
The company admits that its systems 'do not always delete images in a reasonable period of time.'
The news is liable to be a shock to users who've relied on the delete function to remove embarrassing photos from office parties or nights out.
Deleted images vanish from 'normal' views of the site - ie if you log in to Facebook and look on somebody's photo page, they won't be visible - but remain visible to anyone with a direct URL link to the picture.
That means that if, for instance, a picture has been circulated by email, the image will still be there for anyone who clicks the link.
Facebook has repeatedly promised to 'fix' problems with the systems it uses to remove photographs, after users pointed out that images tended to persist after deletion.
Not all deleted pictures are affected, but a significant percentage.
Technology site Ars Technica reports that a picture of a naked toddler supposedly 'removed' in 2008 was still visible as of February 2012.
Site readers reported campaigns of harassment using supposedly 'deleted' pictures.
Facebook has been repeatedly informed of the problem, but the company's line has always been that it is being fixed