I'd like to extend the dexterity image object and add a "Last Accessed Date" field (plone 5.2) which would update anytime it is rendered. I know I can use XML schema to add fields, this is something a little more. Especially since this field needs to update when the object gets rendered. I extended objects back in the archetypes days but I am not sure the best way for dexterity. Most of the documentation only goes as deep as xml.
Why? My staff love uploading images, we have over 1500 now. Some are never used anymore and I want to purge the old ones. I can't tell what is used and what is not.