Something I've been seeing lately is people making a post, adding an image with alt text, (thanks for that, by the way!), but then the alt text is an exact copy of the post. You don't need to do this. If sharing a screenshot of text, then you either don't need to add anything else to it, or you should say something else in your post: explain where it came from, the significance, Etc. If sharing a picture, then the alt text should actually be a description of the picture. Hope this helps.