Announced today (11 Jun 19) by CathyH (lackey) in the geocaching.com forums there has been an update to the logging requirements for an Earth Cache. Geocaching HQ the Geological Society of America and the EarthCache Reviewing Team have worked together to make an update to the EarthCache Guidelines. The Help Center has been updated as well.

Effective immediately, photo requirements are permitted in addition to the regular logging tasks and not as a substitution. The standard for this photo requirement is consistent with the photo requirement for the new virtuals, in that a personal item can be used for those who do not want to photograph themselves.

The update should, according to HQ, make it easier for cache owners to monitor the integrity of the logs on their EarthCaches.

Excerpt from ‘Acceptable Logging Tasks’
Asking geocachers to provide a photo of themselves or a personal item to prove they visited the site.  A personal item must be an option for those who do not want to photograph themselves.  This task is acceptable only as an addition to well-developed logging tasks, not as a substitution.

NOTE: A member of the geocaching community asked if the requirement could be retroactively added to their already published EarthCache. A response from CathyH confirmed that you CAN change your existing EarthCache listing to require a photo as long as the guidelines are followed.