Which websites did you try it on? For a lot of sites, it won't be able to find a larger version, because it's the largest version that the site hosts. It doesn't perform a reverse image search, it complements using one, as often reverse image search engines don't link to the largest version a website hosts (as they have no knowledge of how to do this). If, however, the site should does host a larger version and the script doesn't support it, please let me know!

Just to make sure it's not some bug however, can you check if https://pbs.twimg.com/media/DlOC3mOWsAEi1ld.jpg redirects to https://pbs.twimg.com/media/DlOC3mOWsAEi1ld.jpg?name=orig (or a similar URL)?