Post submissions/edits have a field for text: instead of posting an image of text, simply enter the text in the text field. Keeping the redundant image would be fine, too, though unnecessary. Where it makes sense to keep the image, the Alt Text field in post submissions/edits should be filled.

The text for this image is obvious. Guidelines by web accessibility resources clarify less obvious cases. Screenshots of a social media post should really have the URL field set to the post (or backup) address.