Glass allows sharing photos through Twitter, Dropbox can save them. (As since Glass update XE8, Glass auto-hashtags #throughglass all twitter posted photos.)
If
New tweet by you with hashtag
This Trigger fires every time you post a new tweet with a specific hashtag.
Then
Add file from URL
This Action will download a file at a given URL and add it to Dropbox at the path you specify. NOTE: 30 MB file size limit.
Explore more great ways to automate Dropbox and Twitter