Twitter doesn't do a great job of displaying it, but it's actually embedded in the alt text attribute for the images! This is what it looks like from the logged-in user's perspective[1].
I originally tried to additionally add the full text as a series of replies to the image tweet, but I couldn't get those APIs to work reliably. Perhaps it's worth another try :-)
Author here: that collection has been curated a bit. If you want the entire (scanned) DOCUMERICA collection, it's on the National Archives' website[1].
For example, you could add a nice descriptive text and the date "SMOG OVER INDUSTRIAL HUMBOLDT BAY-EUREKA AREA, 5/1972" to this tweet: https://twitter.com/dailydocumerica/status/14524913223848591...
Either way, very cool content!