I know that they make corrections when they omit or misattribute published graphics; see for example the April 24th Corrections. It includes three separate picture credit corrections.
Further, by viewing the referenced stories, it's clear that the NYTimes also updates the online versions to include the corrected credits. Yet the story which grabbed my graphic still has no online correction.
Perhaps the NYTimes views the Internet and blogosphere as a giant anonymous hive mind from which creative content can be copied and pasted at will without attribution? That's what it's starting to feel like here.