diff -r 56608f42821f -r bff393b23a68 src/iconolab_mcc/management/commands/importimages.py
--- a/src/iconolab_mcc/management/commands/importimages.py	Fri Jun 22 17:34:37 2018 +0200
+++ b/src/iconolab_mcc/management/commands/importimages.py	Sat Jun 23 02:04:20 2018 +0200
@@ -343,7 +343,8 @@
                 item_photo_credits = item['PHOT']
                 item_inventory_number = item['INV']
                 item_joconde_ref = item['REF']
-                if ItemMetadata.objects.filter(item__collection=collection, natural_key=item_joconde_ref).exists():
+                natural_key="%s|%s" % (collection.name,item_joconde_ref)
+                if ItemMetadata.objects.filter(item__collection=collection, natural_key=natural_key).exists():
                     print('#### An item with ' +
                           item['REF']+' for natural key, already exists in database in the import collection')
 
@@ -366,7 +367,7 @@
                             folder = Folder.objects.get(original_id=folder_id)
 
                         item_metadata = ItemMetadata.objects.get(
-                            item__collection=collection, natural_key=item_joconde_ref)
+                            item__collection=collection, natural_key=natural_key)
                         item = item_metadata.item
 
                         item.folders.add(folder)
@@ -388,7 +389,7 @@
                         "joconde_ref" : item_joconde_ref
                     }
                     self.create_item_and_metadata(
-                        item_joconde_ref, collection, new_metadata, item['SRC_IMG_FILES'], options, self.source_dir)
+                        natural_key, collection, new_metadata, item['SRC_IMG_FILES'], options, self.source_dir)
 
             print('# All done!')