diff --git a/tests/test_rendertools.py b/tests/test_rendertools.py
index 39430d670297ac04c7fe9b01bb021889d612a7f0..93452fa2db0400b12c6874bbbf5b51204d8d8ff4 100644
--- a/tests/test_rendertools.py
+++ b/tests/test_rendertools.py
@@ -39,12 +39,11 @@ def checkFrozenImage(sFileImage):
     bytesFrozenImage = None
     for sDir in [ "/images/", "/images/test/" ]:
         sfPath = sDirRoot + sDir + sFileImage
-        with open(sfPath, "rb") as fIn:
-            bytesImage = fIn.read()
-            if bytesFrozenImage == None:
-                bytesFrozenImage = bytesImage
-            else:
-                assert(bytesFrozenImage == bytesImage)
+        bytesImage = plt.imread(sfPath)
+        if bytesFrozenImage is None:
+            bytesFrozenImage = bytesImage
+        else:
+            assert (np.sum(np.square(bytesFrozenImage-bytesImage)))
 
 
 def test_render_env():