ACLs + relations

[michalcharvat]

How I can solve permissions like Websites - Pictures where 1 picture could be used on many websites but I dont want create new picture for each websites. Main acls are on websites however that isnt standard parent/child relation but in this case relations table is necessary. AclItem does not solve this because there is direct relation, websites will be OwnerEntity so I am missing another one which allows you create M:N relation so then you have to ask not via parent relation but via relation table which pictures you are able to see.