From the main screen, tap on your avatar to open the sidebar.
Then choose “Settings and privacy.”
(avatar icon → “Settings and privacy”)
Then choose “Accessibility”
And enable “Compose image descriptions”
So now what?
When you’ve written a tweet that you’d like to add an image to—
Add a photo to your tweet just like you would normally.
But now you’ll notice that there’s an extra button—“Add description” ✨
Tap on that and describe the image as best as you can.
And then tweet it!
“So what do you mean, ‘Describe the image as best as you can’?”
As a rule of thumb—
Think of writing alt text for an image as if you’re describing the image to someone over the phone.
See if you can picture the tweet that’s being described here.
Is this what you pictured?
Here’s the text that went into that description—
alt="Behind World Wildlife Foundation logo panda, a similarly Frank Miller-esque panda stands poised to strike down upon it with one of those metal chairs you'd find at a local AA meeting, his mouth agape with the fury of any WWF wrestler condemning his opponent. Believe it's an illustration by GLENNZ, the most important illustrator of our time."
So all that is to say—
Yeah, it might sometimes take a couple of sentences to fully describe an image.
Suggested potential alt text: Amid a protest march in which many participants are wearing pink hats, a boy enthusiastically holds up a sign that reads 'I [heart] Trains'
Or how might you describe this image?
Potential alt text: Two women stand in a museum, surrounded by sculptures. As one woman proposes to the other, placing a ring on the other woman's finger, an older woman who is sitting nearby looks on with an expression of sheer joy.
Or how about the image on this tweet?
Suggested approach: Transcribe the text within the screenshot verbatim—yup, all of it—and use that as the image’s alt text.
This one may be hard, but how might you approach this?
Suggested approach: Transcribe the text in the image and use as much as will fit within Twitter’s 420-character limit for alt text; then write up a blog post with the full text of the image and include a link to that blog post in the tweet.
So all this stuff is just as easy when you use GIFs, right?
It turns out that Twitter doesn’t support alt text for animated GIFs.
So for tweets with GIFs, your best option is to add a description within the body of the tweet.
Let’s suppose that you had wanted to write a tweet with this GIF—
First up: Write the text of your tweet.
Then add the GIF normally.
Then, after your text, write “alt = ” and a description of the GIF.