diff --git a/prosopopee/cache.py b/prosopopee/cache.py
index 20b3ea0..cbbd79f 100644
--- a/prosopopee/cache.py
+++ b/prosopopee/cache.py
@@ -36,9 +36,26 @@ class Cache(object):
 
         return False
 
+    def image_needs_to_be_oritend(self, source, target, command):
+        if not os.path.exists(target):
+            return True
+
+        if target not in self.cache:
+            return True
+
+        cached_image = self.cache[target]
+
+        if cached_image["size"] != os.path.getsize(source) or cached_image["command"] != command:
+            return True
+
+        return False
+
     def cache_thumbnail(self, source, target, image):
         self.cache[target] = {"size": os.path.getsize(source), "options": image.options}
 
+    def cache_auto_oriented_image(self, source, target, command):
+        self.cache[target] = {"size": os.path.getsize(source), "command": command}
+
     def __del__(self):
         self.json.dump(self.cache, open(self.cache_file_path, "w"))
 
diff --git a/prosopopee/prosopopee.py b/prosopopee/prosopopee.py
index f647b4c..c9d0a65 100644
--- a/prosopopee/prosopopee.py
+++ b/prosopopee/prosopopee.py
@@ -55,10 +55,16 @@ class Image(object):
         if not self.autoorient:
             shutil.copyfile(source, target)
             print source, "->", target
-        else:
-            command = "gm convert %s -strip -auto-orient %s" % (source, target)
+            return ""
+
+        command = "gm convert %s -strip -auto-orient %s" % (source, target)
+
+        if CACHE.image_needs_to_be_oritend(source, target, command):
             print command
             os.system(command)
+            CACHE.cache_auto_oriented_image(source, target, command)
+        else:
+            print "skipped %s since it's already generated (based on source unchanged size and images options)" % target
 
         return ""