Is it ironic that a text image is used by Twitter to bypass character limits on a post? This has to be a usability nightmare for differently abled people.
- to "retweet" without notifying the person and being linked to as a "quote tweet" on the OP
- to share a post in a controversial context where many people are blocked by the tweeter in question (if you're blocked by someone, you can't read their tweets)
- to share a post you expect will be deleted shortly
- to screengrab a couple of posts that make up necessary context and wouldn't make sense if retweeted on their own
To your point about people using screenreaders etc, it seems to me that it would be fairly trivial (cputime aside) to OCR tweets and automatically apply alt-text, but instead they rely on the uploader to enter it manually.