Embed image as default

Embed image as default to work in qtconsole unless url kwarg is set
explicitely

fixes  #1614

IPython/core/display.py

@@ -422,7 +422,7 b' class Image(DisplayObject):'
 
     _read_flags = 'rb'
 
-    def __init__(self, data=None, url=None, filename=None, format=u'png', embed=False):
+    def __init__(self, data=None, url=None, filename=None, format=u'png', embed=None):
         """Create a display an PNG/JPEG image given raw data.
 
         When this object is returned by an expression or passed to the
@@ -441,10 +441,24 b' class Image(DisplayObject):'
             The format of the image data (png/jpeg/jpg). If a filename or URL is given
             for format will be inferred from the filename extension.
         embed : bool
-            Should the image data be embedded in the notebook using a data URI (True)
-            or be loaded using an <img> tag. Set this to True if you want the image
-            to be viewable later with no internet connection. If a filename is given
-            embed is always set to True.
+            Should the image data be embedded using a data URI (True) or be
+            loaded using an <img> tag. Set this to True if you want the image
+            to be viewable later with no internet connection in the notebook.
+
+            Default is `True`, unless the keyword argument `url` is set, then
+            default value is `False`.
+
+            Note that QtConsole is not able to display images if `embed` is set to `False`
+
+        Examples
+        --------
+        # embed implicitely True, works in qtconsole and notebook
+        Image('http://www.google.fr/images/srpr/logo3w.png')
+
+        # embed implicitely False, does not works in qtconsole but works in notebook if
+        # internet connexion availlable
+        Image(url='http://www.google.fr/images/srpr/logo3w.png')
+
         """
         if filename is not None:
             ext = self._find_ext(filename)
@@ -460,7 +474,7 b' class Image(DisplayObject):'
             if ext == u'png':
                 format = u'png'
         self.format = unicode(format).lower()
-        self.embed = True if filename is not None else embed
+        self.embed = embed if embed is not None else (url is None)
         super(Image, self).__init__(data=data, url=url, filename=filename)
 
     def reload(self):