diff --git a/exp/kerokero/prepare_data.py b/exp/kerokero/prepare_data.py
--- a/exp/kerokero/prepare_data.py
+++ b/exp/kerokero/prepare_data.py
@@ -81,8 +81,8 @@ def harvestDir(path):
 		img=cv.cvtColor(img,cv.COLOR_BGR2GRAY)
 		for b in boards:
 			sample=Sample(img,b.grid)
-			(img,label)=sample.transform()
-			yield (img,label)
+			(transformedImg,label)=sample.transform()
+			yield (transformedImg,label)
 
 
 def loadDataset(root):