Twitter confirmed that the images are part of the social media company's experiment with ways to tackle misinformation on its platform.
"This is a design mock-up for one option that would involve community feedback," a Twitter spokesperson told ABC News. "Misinformation is a critical issue, and we will be testing many different ways to address it."
Based on the images, the feature would append a bright orange label including the words "Harmfully Misleading" if the tweet is flagged as containing mis- or disinformation.
The images are only early-stage mock-ups and not a feature currently being tested within Twitter, a source at Twitter told ABC News.
On March 5, Twitter said the company is planning a series of updates to its platform to target misinformation. These include applying a label to tweets that have been "have been significantly and deceptively altered or fabricated," showing a warning to people before they retweet or like the tweet, and reducing the tweet's visibility, according to a Twitter blog post.
The leaked mock-up images are not a part of that March update, according to a Twitter source.