diff --git a/src/calibre/ebooks/oeb/polish/images.py b/src/calibre/ebooks/oeb/polish/images.py
index f20e49d1c6..49e75bc52c 100644
--- a/src/calibre/ebooks/oeb/polish/images.py
+++ b/src/calibre/ebooks/oeb/polish/images.py
@@ -54,8 +54,14 @@ class Worker(Thread):
             func = partial(encode_jpeg, quality=self.jpeg_quality)
         path = self.container.get_file_path_for_processing(name)
         before = os.path.getsize(path)
+        with lopen(path, 'rb') as f:
+            old_data = f.read()
         func(path)
         after = os.path.getsize(path)
+        if after >= before:
+            with lopen(path, 'wb') as f:
+                f.write(old_data)
+            after = before
         self.results[name] = (True, (before, after))
 
 
@@ -89,12 +95,14 @@ def compress_images(container, report=None, names=None, jpeg_quality=None, progr
         name = force_unicode(name, filesystem_encoding)
         if ok:
             before, after = res
-            if before != after:
-                before_total += before
-                after_total += after
-                if report:
+            before_total += before
+            after_total += after
+            if report:
+                if before != after:
                     report(_('{0} compressed from {1} to {2} bytes [{3:.1%} reduction]').format(
                         name, human_readable(before), human_readable(after), (before - after)/before))
+                else:
+                    report(_('{0} could not be further compressed').format(name))
         else:
             report(_('Failed to process {0} with error:').format(name))
             report(res)