Isis Wenger, 22, a platform engineer in San Francisco, got talked into being one of a handful of colleagues featured in a hastily organised recruiting ad campaign for her company OneLogin, she wrote on Medium.
The response shocked her. Friends forwarded her posts from complete strangers responding to the photo, and soon they didn't need to send them - they were everywhere.
"If you knew me you would probably know that being famous is one of my biggest nightmares; seriously right up there with falling into a porta potty," she wrote.
Still, there was her image, triggering all this reaction - a lot of it negative. And a lot of it mirroring attitudes she often saw in the tech world, she wrote - from men who seemed like pretty smart and normal guys who didn't know how uncomfortable their comments might make someone.
She ended the post with a challenge: "Do you feel passionately about helping spread awareness about tech gender diversity?
"Do you not fit the 'cookie-cutter mould' of what people believe engineers 'should look like'? If you answered yes to any of these questions, I invite you to spread the word and help us redefine 'what an engineer should look like' #iLookLikeAnEngineer."
And she posted a photo of herself with the hashtag.
It took off.
"Especially when I was first starting out in the industry, people were very condescending. There's no way I could have been an engineer, right? They had pretty low expectations of me."
But growing up, the only child of a single mother, a teacher, she had already taught herself to build websites by the time she was 8, by right-clicking "view source on Neopets and reverse-engineering bits of code to figure out what each individual tag did".
If colleagues had low expectations, she quickly showed them up.
Soon #Ilooklikeanengineer tweets came from women all over the world (and a few men, and others), tired of surprised looks when they met a client for the first time, or arrived at an interview.
Small wonder Wenger is "experiencing a lot of cognitive dissonance". As a soft-spoken but strong-willed person, "It's simultaneously overwhelming and incredibly empowering to feel I'm genuinely helping increase awareness."

