anchor.diff:        final Option<Item> sourceItem = await _itemDataSource.getById(itemId);
   
         if (sourceItem.isEmpty) return;
  +
         if (!MimeTypes.imageTypes.contains(sourceItem.first.mime)) return;
   
  +      if(startPoint==null)
  +        startPoint = sourceItem.first.uploaded;
   
  -
  +      _log.info("Checking for item $itemId starting with $startPoint");
  +      
         final ImageHash sourceHash = await _getPerceptualHash(itemId);
   
  -      final Stream<Item> itemStream = await _itemDataSource.streamAll(limit: 100, startDate: startPoint, addedDesc: true);
  +      final Stream<Item> itemStream = await _itemDataSource.streamAll(limit: 500, startDate: startPoint, addedDesc: true);
         DateTime lastProcessedDate;
         await for (Item targetItem in itemStream) {
           lastProcessedDate = targetItem.uploaded;
  
positive.code:           }
        }
        if(lastProcessedDate!=null) {
          await _backgroundQueueDataSource.addToQueue(this.extensionId, "$itemId:$lastProcessedDate", priority: item.priority+1);
        }
  
  
negative.code:         new ImageHash.forImage(decodeImage(f.readAsBytesSync()), size: 16);
  
      final String perceptualHash = imageHash.toString();
      _log.info("Perceptual hash: $perceptualHash");
  
      final ExtensionData newData = new ExtensionData();
      newData.extensionId = extensionId;
  