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

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.

• Mark Hamill's cameo broke Big Bang Theory star Mayim Bialik
• Sam Heughan and Caitriona Balfe had insane chemistry in their first Outlander screen test
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https://www.youtube.com/watch?v=witDdhvd8Fw&list=PLbs-Pk9dtKb8YP3Qd5UDiUQqkuzd776iF

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

https://www.instagram.com/p/BiHEQ4DHch7/?hl=en&taken-by=samheughan

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

https://www.instagram.com/p/BiGZ3Rqhoo6/?hl=en&taken-by=emmawatson

And John Barrowman...

https://www.instagram.com/p/BiF2424lEsi/?hl=en&taken-by=johnscotbarrowman

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

https://twitter.com/HamillHimself/status/990047697586479104

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

https://www.instagram.com/p/BiGFWL1h_hf/?hl=en&taken-by=sanctionedjohnnygalecki

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

https://www.instagram.com/p/BiFosRVHScU/?hl=en&taken-by=reesewitherspoon

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

https://www.instagram.com/p/BiFcB23BHuI/?hl=en&taken-by=melissamccarthy