transform_image wcs update
Sorry if this is a silly question, but where in transform_image does the wcs get updated after the transformation is done?  I don't see anything in the code that looks like it's doing this, but maybe that's somewhere else in the data class? This isn't really high priority or anything, I was just curious.

http://ccdproc.readthedocs.io/en/latest/_modules/ccdproc/core.html#transform_image

Thanks!
diff --git a/CHANGES.rst b/CHANGES.rst
index 6eed498..0fdc212 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -28,6 +28,8 @@ Other Changes and Additions
 
 - Added support for .bz2, .Z and .zip file formats in ``ImageFileCollection``.
 
+- Added warning that ``transform_image`` does not apply the transformation to the WCS [#684]
+
 - Removed support for initializing ``ImageFileCollection`` from a table instead
   of files. [#680]
 
diff --git a/ccdproc/core.py b/ccdproc/core.py
index 58ca662..a13cf65 100644
--- a/ccdproc/core.py
+++ b/ccdproc/core.py
@@ -2,10 +2,13 @@
 
 """This module implements the base CCDPROC functions"""
 
+import math
 import numbers
+import logging
 
 import numpy as np
-import math
+from scipy import ndimage
+
 from astropy.units.quantity import Quantity
 from astropy import units as u
 from astropy.modeling import fitting
@@ -16,12 +19,12 @@ from astropy.wcs.utils import proj_plane_pixel_area
 from astropy.utils import deprecated
 import astropy  # To get the version.
 
-from scipy import ndimage
-
 from .utils.slices import slice_from_string
 from .log_meta import log_to_metadata
 from .extern.bitfield import bitfield_to_boolean_mask as _bitfield_to_boolean_mask
 
+logger = logging.getLogger(__name__)
+
 __all__ = ['background_deviation_box', 'background_deviation_filter',
            'ccd_process', 'cosmicray_median', 'cosmicray_lacosmic',
            'create_deviation', 'flat_correct', 'gain_correct', 'rebin',
@@ -853,6 +856,10 @@ def transform_image(ccd, transform_func, **kwargs):
         mask = transform_func(nccd.mask, **kwargs)
         nccd.mask = mask > 0
 
+    if nccd.wcs is not None:
+        warn = 'WCS information may be incorrect as no transformation was applied to it'
+        logging.warning(warn)
+
     return nccd
 
 
diff --git a/ccdproc/tests/test_ccdproc.py b/ccdproc/tests/test_ccdproc.py
index f61c2be..c8f6721 100644
--- a/ccdproc/tests/test_ccdproc.py
+++ b/ccdproc/tests/test_ccdproc.py
@@ -573,6 +573,15 @@ def test_transform_isfunc(ccd_data):
     with pytest.raises(TypeError):
         transform_image(ccd_data, 1)
 
+#test warning is issue if WCS information is available
+def test_catch_transform_wcs_warning(ccd_data):
+
+    def tran(arr):
+        return 10 * arr
+
+    with catch_warnings() as w:
+        tran = transform_image(ccd_data, tran)
+
 
 @pytest.mark.parametrize('mask_data, uncertainty', [
                          (False, False),
['ccdproc/core.py', 'ccdproc/tests/test_ccdproc.py', 'CHANGES.rst']