diff --git a/beets/mediafile.py b/beets/mediafile.py
index 1ac589536..ec14f99e9 100644
--- a/beets/mediafile.py
+++ b/beets/mediafile.py
@@ -756,9 +756,9 @@ class ImageField(object):
             return None
 
         else:
-            # Here we're assuming everything but MP3, MPEG-4, and FLAC
-            # use the Xiph/Vorbis Comments standard. This may not be
-            # valid. http://wiki.xiph.org/VorbisComment#Cover_art
+            # Here we're assuming everything but MP3, MPEG-4, FLAC, and
+            # ASF/WMA use the Xiph/Vorbis Comments standard. This may
+            # not be valid. http://wiki.xiph.org/VorbisComment#Cover_art
 
             if 'metadata_block_picture' not in obj.mgfile:
                 # Try legacy COVERART tags.
@@ -775,7 +775,7 @@ class ImageField(object):
             else:
                 return None
 
-            if pic.data == '':
+            if not pic.data:
                 return None
 
             return pic.data
diff --git a/test/rsrc/full.opus b/test/rsrc/full.opus
index 81cd65284..9a5534b22 100644
Binary files a/test/rsrc/full.opus and b/test/rsrc/full.opus differ
diff --git a/test/test_mediafile_basic.py b/test/test_mediafile_basic.py
index af54ee717..3cbee09e7 100644
--- a/test/test_mediafile_basic.py
+++ b/test/test_mediafile_basic.py
@@ -175,7 +175,7 @@ READ_ONLY_CORRECT_DICTS = {
 
     'full.opus': {
         'length': 1.0,
-        'bitrate': 63216,
+        'bitrate': 57984,
         'format': 'Opus',
         'samplerate': 48000,
         'bitdepth': 0,