A belated word about last week's Facebook fiasco, if I may. You might remember the company aroused all sorts of excitement when it changed its terms and conditions to allow itself rights in perpetuity to images on its servers. The BBC had a social media expert in to explain how the company was getting a little above itself.

I should declare an interest, albeit an indirect one; I've just been asked to write a book on social media. I know a little about what I'm talking about. So, of course, does this guy.

He doesn't mention, though, the obvious reason Facebook should want to extend its rights. If I log on to the website and look at an image, it's on my computer in the cache, at least for a while. Facebook has to be allowed to authorise me to make that copy, even temporarily.

And if I decide to keep the copy, probably by right-clicking and something or other, I've taken a permanent copy from Facebook. For the company to allow this without becoming liable for copyright infringement, it has to allow me to make and keep a copy. It needs to be authorised to let me keep that copy, even once the picture is off its servers.

So yes, there are entirely benign reasons that could explain the so-called rights grab. I'll be interested to see what they come up with to replace the idea.