Therefore, there was no grandfathering of older EarthCaches that required a photo to be posted in order to get credit for the find. When the requirements were changed, there was a review of existing EarthCaches to notify those who had such a requirement to make it optional or remove it. However, it is possible that some EarthCaches were missed or that the owner did not make the requested change and there was no followup by the reviewer. So, if posting of a photo is the ONLY requirement for this EarthCache, then you should probably comply and post your picture. After all, it sounds like you have taken it! But then send an email to the EarthCache reviewer who published the listing to let them know that about the situation so that they can get the owner to remove the requirement for a photo (or make it optional) and to update their listing with logging requirements that satisfy the educational intent of this type of cache.
7. Requests for photographs must be optional. Exceptions to this guideline will only be considered if the requested photograph is related to an Earth Science logging activity such as recording a phenomenon. This particular guidelines was updated on 1 January 2011. All EarthCaches must conform to this guideline as photo requests are considered "optional tasks" and follow the guidelines set forth by Geocaching.com.
Existing EarthCaches that do not meet this guideline must be updated to comply. Cache owners may not delete the cacher's log based solely on optional tasks.