OMG I don't look like that. I recoiled in horror as my mate Whatsapped me a photo she'd taken over the weekend. I over-analysed every inch of my body, zooming in on my thighs and my belly and my chin.

As I'd been getting ready that morning, the reflection that stared back at me from the mirror didn't look like this version of myself that my friend had managed to capture. My body also looked like an entirely different body from the one that I'm used to seeing on my phone screen in selfies. The ones that I post on Instagram.

So, this morning, when I logged on for my morning scroll, I felt so seen when I came across body confidence influencer Alex Light's latest post – in which she shares a selfie and a photograph that someone else has taken of her side-by-side. Her body looks different sizes in each of the pictures, yet she goes on to explain that she's the exactly the same clothes size and weight in each, but that there's "science" behind why she looks different in each of the images.

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"I have been posting lots of mirror shots recently," says Alex in the caption. "And I’ve received so many DMs either telling me that I look like I’ve lost weight, asked whether I’m trying to lose weight or admitting that they’re envious that I look slim."

"In an ideal world," she continued, "we would look at a picture of someone and not even notice their body size, I appreciate this is currently wishful thinking. With that in mind, I feel compelled to point out that you cannot compare yourself to a picture of someone."

She goes on to point out that in the photos that are posted side by side for comparison, she is exactly the same size and weight – "literally the same body," she writes. Then she acknowledges that there's actually a reason for it, that it's often "angles" and also "different methods of shooting."

The post has already garnered more than 17,000 likes in the space of hours, so it's clearly very relatable content. And the comments have gone wild. "I really struggle with looking at pictures of me taken by others because I feel like I look too wide. Whenever I look in a mirror/take a mirror selfie I feel like I look like myself. But when I see pictures others take of me I always get insecure on whether I really look like that or not 😢," said one commenter.

Photographer Nadia Meli, was quick to jump in on the debate explaining that in her expert opinion, there's a very good reason as to why we look different. "Omg yes, as a photographer this always drives me crazy: but we do look different through different lenses!

"Our bodies and faces do not look the same in the mirror, on a professional DSLR, on the phone camera, the front lens the back lens - all of these don't show us how we actually look either! Lenses always flatten us, it's just 2D, not 3D and doesn't give an accurate representation of what we see when someone is in front of us IRL! I always tell my clients to chill and not take what they see in their photos too seriously."

When I slid into Nadia's DMs to find out more, she said that as a photographer she's obsessed with faces because she studies them all the time. "One of the fascinating things about my work is the failure of the camera to actually capture what truly is in front of me," she explained. When she started paying close attention to the small details – for example a nose or a chin – she realised that the photo never matched what she could see in front of her. "People usually look a bit wider and more flat than in real life," she said. "Even camera phones – they just don’t reflect what we really see."

And another photographer, Fever Dream, went on to say: "Camera lenses and focal lengths can change the shape of faces causing them to appear more round or thinner even when shot from a similar [distance]. When factoring in that with a mirror, there can also be variations in the way the glass refracts the light.

"Lastly, it can be shocking to see ourselves from a perspective our own eyes did not deliver and sometimes it challenging when we're not used to having our picture taken by someone else."

As Alex succinctly writes at the end of her post, "It’s an unfair comparison and you don’t deserve or need it!" Which is a mantra we can very much get on board with... and if you need some more of her wise words in your life, Alex's book You Are Not A Before Picture is out on 9 June.

You Are Not a Before Picture by Alex Light

You Are Not a Before Picture by Alex Light

You Are Not a Before Picture by Alex Light

£15 at harpercollins.co.uk