A short note on why this letter exists.

You've probably already seen it today. You woke your phone and the lock screen had changed overnight — a new photograph of somewhere cold and blue. You looked something up, and above the search box sat a little drawing that wasn't there yesterday. Maybe you gave it two seconds. Tomorrow it will be gone.

But the picture wasn't random. Someone chose it for today, sometimes months in advance. Today is a scientist's birthday. Today a railway opened, a treaty was signed, a bird began its migration south. The image sits there like an unsigned note left on the world's desk: something about today matters. A few billion people see the note. Almost nobody has time to ask the obvious question — why today?

We decided to make asking it our job.

The Daily Backstory is a short daily letter about one image the world woke up to — Google's Doodle, Bing's wallpaper, NASA's astronomy picture, the photograph Wikipedia or National Geographic or the Guardian chose to put in front of everyone. Whichever picture carries the best story that day, we tell it: what you're looking at, who made it, and why it appeared on this date and not another.

A word about the word. "Backstory" is about as plain as English gets — it's what you ask for at a yard sale, not in a lecture hall. That's deliberate. Curiosity shouldn't require credentials. The homepage may be the most democratic gallery ever built: no ticket, no velvet rope, the same picture for a billion strangers on the same morning. We think the story behind the picture should be just as free — dug up, checked, and told in plain language, in the time it takes to finish a coffee.

We don't expect a five-minute email to change your life. But people who know backstories start to see differently. The same stretch of ocean, once you know which ocean and why it surfaced today, is never quite the same ocean. Days work like this too. All 365 of them look alike until you learn that each one is somebody's anniversary, some creature's departure date, some idea's birthday. Collect enough of them and you end up with something like a family album for the calendar.

One more thing: this letter has a Chinese-language twin, 《来历》 — laili, the word your grandmother would use when asking about an old object's origins. Same newsroom, different voice.

One image a day. The picture is already on your screen; we'll bring the story.

Every image has a backstory. See you tomorrow.