{ "rules_verify_pictures_removed" : {
    "LABEL" : "Verify pictures removed",
    "PLUGIN" : "reaction rule",
    "OWNER" : "rules",
    "TAGS" : [ "image" ],
    "REQUIRES" : [ "rules_conditional", "rules" ],
    "ON" : { "node_update--article" : { "bundle" : "article" } },
    "DO" : [
      { "LOOP" : {
          "USING" : { "list" : [ "node-unchanged:field-pictures" ] },
          "ITEM" : { "list_item" : "Previous list item" },
          "DO" : [
            { "CONDITIONAL" : [
                {
                  "IF" : { "NOT list_contains" : { "list" : [ "node:field-pictures" ], "item" : [ "list-item" ] } },
                  "DO" : [
                    { "drupal_message" : { "message" : "Picture has been removed.", "type" : "warning" } }
                  ]
                }
              ]
            }
          ]
        }
      }
    ]
  }
}