His official Twitter account posted a four-picture photo grid showing cabinet members having a meeting.
The alt text fields - which are supposed to describe what's in the images for blind users - simply read: "We're growing the economy".
Number 10 said it "aims to ensure" images are "as accessible as possible".
Just two weeks ago, companies like McDonald's were criticised for posting the "click here" meme, which used alt text to hide jokes.
The accessibility feature works with screen readers and is supposed to describe image elements like what people are wearing, their surroundings, and any text that appears.
When photos in the tweet from Rishi Sunak's account are clicked, each expands to reveal a list of things the government says it has done.
But because this information is not included in the alt text, anyone using a screen reader will not know what it says.
The government's received backlash for not fully describing the images.
Becky says it's especially bad from Rishi Sunak because the government published guidance for public bodies to make their websites and apps accessible in 2018.
"I know that the guidance doesn't specifically reference social media," she says.
"But I think it's reasonable to expect that communications teams of a key public figure such as the prime minister also makes their social media posts accessible."
In a statement, Number 10 said: "We use a broad range of methods and channels to communicate with the public and aim to ensure that they are as accessible as possible.
"That includes using alternative text on our social channels."