Doctor Who, Harry Potter and Outlander stars share their oldest head shots

We all have embarrassing photos, but most of us like to bury them in an old photo album or in the depths of our Facebook archive.

If you've spent your life on screen it's a little different. Actors from across the world of film and television have been making some seriously old snaps public in aid of #oldheadshotday – a hashtag that has been doing the rounds on social media.

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The baby-faced throwback photos have been shared by the likes of Sam Heughan...

... Emma Watson (who demonstrates her strong hat game):

And John Barrowman...

Star Wars actor Mark Hamill shared a whole series of youthful snaps.

And The Big Bang Theory's Johnny Galecki is sporting a heap of hair:

Oscar-winner Reese Witherspoon doesn't look all that different.

While Melissa McCarthy demonstrated her, er, range from an early age...