What's happened to contact images in 5.8.2?
I'm pretty sure that that this problem wasn't caused by the update to 5.8.2 but instead the installation of the Shoredtich extension as part of installing Mosaico. This issue clarifies: https://github.com/civicrm/org.civicrm.shoreditch/issues/374 

Essentially there is a JS file in the Shoreditch extension - contact-summary.js - that is loading on every page regardless of whether Shoreditch has been installed purely to support Mosaico (as in my case).