Just add a photo to your "Twitter" album and they will automagically post.
If
New photo added to album
This Trigger fires every time a new photo is added to the album you specify.
Then
Post a tweet with image
This Action will post a new tweet to your Twitter account with a linked pic.twitter.com image. NOTE: Please adhere to Twitter’s Rules and Terms of Service.
Discover more time saving integrations for Twitter and iOS Photos