Twitter started rolling out its Facebook-a-like header photos to profiles back in September, and users who haven’t yet implemented this new functionality have until tomorrow (December 12th) to upload a suitable image.

Otherwise, Twitter is going to force the change upon you, and you’ll be left with a default grey box.

This isn’t permanent – you can change your header photo at any time. But, as Twitter says, the grey background isn’t exactly fun. Although, let’s be honest, neither are the header photos. They’re pretty limiting, and while a few folks have made an effort, they’re very much in the minority.

And to be honest, because you have no control over the colour, style and placement of the font that displays your Twitter bio over your photo, a blank, grey box probably isn’t the worst thing in the world, as at least your text will be legible.

You can check out how it will look below if you take no action whatsoever.

Still, if you’re feeling inspired, and in case you missed it, Twitter has released this video to help you on your way.

(Source: Twitter blog.)