Added default_image_field

This works kind of like Django's models' _default_manager. If your specs don't
specify an image_field, and your IKOptions don't specify a default_image_field,
the first ImageField your model defines will be used.

imagekit/models.py

@@ -41,14 +41,18 @@ class ImageModelBase(ModelBase):
     """
     def __init__(self, name, bases, attrs):
         user_opts = getattr(self, 'IKOptions', None)
-        
         specs = []
+        default_image_field = getattr(user_opts, 'default_image_field', None)
+        
         for k, v in attrs.items():
             if isinstance(v, ImageSpec):
                 setattr(self, k, Descriptor(v, k))
                 specs.append(v)
-        
+            elif not default_image_field and isinstance(v, models.ImageField):
+                default_image_field = k
+
         user_opts.specs = specs
+        user_opts.default_image_field = default_image_field
         opts = Options(user_opts)
         setattr(self, '_ik', opts)
         ModelBase.__init__(self, name, bases, attrs)

imagekit/options.py

@@ -10,8 +10,16 @@ class Options(object):
 
     admin_thumbnail_property = 'admin_thumbnail'
     """The name of the spec to be used by the admin_thumbnail_view"""
-    
-    image_field = 'image'
+
+    default_image_field = None
+    """The name of the image field property on the model.
+    Can be overridden on a per-spec basis by setting the image_field property on
+    the spec. If you don't define default_image_field on your IKOptions class,
+    it will be automatically populated with the name of the first ImageField the
+    model defines.
+
+    """
+
     crop_horz_field = 'crop_horz'
     crop_vert_field = 'crop_vert'
     preprocessor_spec = None

imagekit/specs.py

@@ -15,7 +15,7 @@ from django.core.files.base import ContentFile
 
 class ImageSpec(object):
 
-    image_field = 'original_image' # TODO: Get rid of this. It can be specified in a SpecDefaults nested class.
+    image_field = None
     processors = []
     pre_cache = False
     quality = 70
@@ -27,7 +27,8 @@ class ImageSpec(object):
         self.__dict__.update(kwargs)
 
     def _get_imgfield(self, obj):
-        return getattr(obj, self.image_field)
+        field_name = getattr(self, 'image_field', None) or obj._ik.default_image_field
+        return getattr(obj, field_name)
 
     def process(self, image, obj):
         fmt = image.format