Happy #WorldSightDay!
To promote the importance of accessibility on social media, I'd like to propose a community action: When you see an image posted on your feed without alt text, instead of boosting it, or asking the person who posted it to add it, consider replying with your own description, together with the hashtag "Alt4You".
Trouble writing alt text for your own images? Tag your post with "Alt4Me", and someone will help you out!