Adding alt text (and more) to images in Mastodon

Getting your Trinity Audio player ready...
3 min read

April 27 2022 update: I originally wrote this post in late 2020 but it sat in my unpublished drafts page and never got published. Today with the influx of new users joining Mastodon it seems like it might be useful so here it is – straight from the draft pile.

April 29 2022 update: Alan Levine pointed me to the Please Caption bot on Mastodon. Follow the bot and when you go to post on Mastodon it will check to make sure you have an alt tag on your photo. Handy reminder that shows how useful bots can be.

A while back our BCcampus accessibility champion Josie Gray hosted an internal workshop on accessibility that was chock-a-block full of wonderful accessibility tips, including a reminder on how to add alt text to social media posts. It is something that I have been trying to do more and more as part of my social media workflow.

Like Twitter, Mastodon does provide the ability to add alt text to images to make them more accessible.

When you upload an image to Mastodon, an Edit icon appears in the top right-hand corner of the image.

Screenshot of Mastodon post with a photo showing location of Edit button in top right corner of photo to add alt text

Click the edit button and you get an Edit Media popup window where you can add in some descriptive alt text.

Mastodon screen shot of the edit media popup showing where to add alt text to an image

There is also a feature of sharing media on Mastodon that makes it different and, IMO, better than Twitter. Remember that incident a few years ago where Colin Madland noticed Twitter would automatically crop photos in odd ways? It was part of the thread where he talked about Twitter’s inability to recognize black faces (which is a different and deeply problematic issue than bad cropping decisions and one you should read more about if you are not familiar with the racial bias in AI algorithms). But here is the bit in Colin’s thread where he noticed the odd cropping decisions automagically made by the Twitter AI.

Well, in Mastodon, you can choose exactly what part of the photo you want to have focus when you share it. See that little circle in the middle of the photo you are sharing? In Mastodon, move that circle around and the preview image in Mastodon will move the focus to that area.

Video demonstrating how you can move a focal point around the screen

There is also an option to tag an image as containing sensitive content when you post.

Screenshot of Mastodon showing location of sensitive image warning toggle located at the botom of a photo that is about to be shared

When this image appears in someone’s feed, it will automatically be blurred out and contain a CW (Content Warning) giving that person the option to decide on whether to see the image or not. Content Warnings are a great feature of Mastodon and you will likely see them often if you spend any length of time on the platform.

Theme by Anders Norén