“Alt alts” is designed to get anyone who posts images online to add an alt text description and, crucially, one that is thorough in its explanation.

Accordingly, the out-of-home campaign uses written descriptions of famous images that passers-by then have to guess.

For instance, one execution says: “A naked young woman swims on the surface, unaware of the sleek, powerful dome of death that rushes up towards her.”

At the bottom of each poster is the copy: “Alt text paints pictures for those who can’t see. Scan to reveal the image.” Readers are urged to scan a QR code, which reveals… nothing.

Instead a message reads: “If you guessed the image, lucky you. For the 2.2 billion people in the world with sight loss, it’s not that easy.  Writing a description to every image you post gives people with sight loss access to the whole picture.”

Alt text, which stands for “alternative text”, helps people with impaired vision gain a mental impression of a visual element, be that a photo or illustration. It is relied on by the two million people in the UK with sight loss.

The campaign is begins with a 96-sheet at Old Street in London, just metres from Moorfields Eye Hospital, and is appearing at various other sites across the UK capital. The OOH is being supported with social activity.

Martin Wingfield, RNIB’s director of brand, said: “Alt text is a hugely important accessibility tool designed to help people navigate the internet more easily. Our ‘Alt alts’ campaign highlights how inclusive content is just good content and ensures you aren’t excluding anyone. Our motto is always to think of accessibility as a love note – it tells people we want you here as well.”

Nicky Bullard, MullenLowe’s group chief creative officer, said: “When I think about the impact certain images have had on me, the thought that we are excluding blind and partially sighted people from feeling the impact of those images makes me very, very sad. This campaign is the start of a massive conversation that must continue.”

The creatives were Jane Briers and Dave Cornmell. Media was by Wavemaker.