Add a description to an image
A description is the alt text people using a screen reader hear in place of your picture; write it once on the file and it travels to every destination that takes one.
Last updated- Open Media Library and select the image.
- In Details, find Description. It reads Not described yet until you write one.
- Say what the picture shows, then save. It reads Described afterwards.
- Attach the image to a post as usual. The description comes with it.
Where the composer reminds you
When you press Schedule and an attached image has no description, the composer pauses: "One image in this post has no description." (or the number of images). You can choose Schedule anyway, which is the primary button, or Add descriptions first. The reminder never blocks you; it only makes the choice visible.
Videos do not take a description in the library.
Platforms differ
Not every platform carries image descriptions. Where one does not, the preview says so, and your description stays on the file for the channels that take one. Where a platform publishes a shorter description than the one you wrote, that channel gets the post without it, and the preview tells you to shorten the description to send it there too.
The field hint says it best: say what the picture shows, for people who cannot see it. Skip "image of".
If it did not work
If you cannot edit the description, your role may not allow changes to library files; it is then shown as read only. If a description does not appear on a platform, that platform may not support it, or it was over the platform's limit. The alt text guide and the alt text checker help you review a batch before you schedule.