I would really appreciate if this Garmin-Feature would be added for Geocaching.com too.
From a Garmin-blog I know, that this feature is already supported by another Caching-Website, but I'm not allowed to link there, as it could be misunderstood as a sort of advertisment. Anyway, from that blog it seems that on the other website it's solved by four download choices for a cache: With all photos, spoilers and required ones only, required ones only, none. A similar solution may do that job here too, if the cache owners would mark their photos as spiolers and/or required ones.