The issue is, when you click on any of those links or try a search query, you won't get results.
For example a search on either [1860s US Civil War source:life] or [Franklin D. Roosevelt source:life], which are featured sample searches, return nothing. Instead it reads, "Your search - Franklin D. Roosevelt source:life - did not match any documents." Here is a picture:
Google has literally taken the life out of the LIFE image search feature.
The thing is, a site command, as opposed to a source command works. Try [Franklin D. Roosevelt site:life.com].
Jeff from Google confirmed the bug in a Google Web Search Help thread. Jeff said:
I appreciate you taking the time to post this issue. I've brought it up with the team and we are investigating.
There is no ETA for a fix but it still does not work for me. Hat tip to Gary Price for pointing this out to me.
Forum discussion at Google Web Search Help.