With the recent news that the r/blind community has migrated to a lemmy instance, I thought now would be a good time to post a quick PSA on image descriptions.
Blind and low vision computer users often rely on screen readers to navigate their computers and the internet. These tools work great on text-based platforms (when the backend is coded correctly to make buttons and UI elements visible to the screen reader), but they struggle a lot with images. OCR and image recognition have come a long way, but they're still not reliable.
On Lemmy, there's no way (yet) to add alt text to image posts, but one thing that we sighted folk can do to make the website a more accessible place for the blind/low vision community is to describe the contents of the image in text, so screen readers (or braille displays) can interpret the text for the user. This doesn't need to be anything fancy - you can see an example of me doing so in this post here - simply indicate somewhere that you are describing the contents of the image, and then do so in text. If you're transcribing text, it's best to do so as exact to the text in the image as you can (including spelling errors!). If you're describing something visual, it's best to keep it about the length of a tweet, but be as detailed as you need to be to give context to what you write about in the post.
If you'd like a more detailed guide on how to best do image descriptions and alt text, here's a site that describes more specifics - https://www.perkins.org/resource/how-write-alt-text-and-image-descriptions-visually-impaired/
Edit: You are able to add alt text to embedded images, as noted by @sal@mander.xyz here. This would only work for images within the text of your comment, not for image posts (topics which link to images).
Edit 2: @retronautickz@beehaw.org wrote a post on kbin on best practices in writing image descriptions and alt text.