Index: wp-content/themes/twentythirteen/css/ie.css
===================================================================
--- wp-content/themes/twentythirteen/css/ie.css	(revision 23659)
+++ wp-content/themes/twentythirteen/css/ie.css	(working copy)
@@ -107,8 +107,7 @@
 	border: 0;
 }
 
-.ie8 img.size-full,
-.ie8 img.size-large {
+.ie8 img {
 	height: auto;
 	width: auto;
 }
Index: wp-content/themes/twentythirteen/style.css
===================================================================
--- wp-content/themes/twentythirteen/style.css	(revision 23659)
+++ wp-content/themes/twentythirteen/style.css	(working copy)
@@ -658,30 +658,8 @@
 
 /*
  * Responsive images
- *
- * Fluid images for posts, comments, and widgets
  */
-.entry-content img,
-.entry-summary img,
-.comment-content img,
-.widget img,
-.wp-caption {
-	max-width: 100%;
-}
-
-/* Make sure images with WordPress-added height and width attributes are scaled correctly. */
-.entry-content img,
-.entry-summary img,
-.comment-content img[height],
-img[class*="align"],
-img[class*="wp-image-"],
-img[class*="attachment-"] {
-	height: auto;
-}
-
-img.size-full,
-img.size-large,
-img.wp-post-image {
+img {
 	height: auto;
 	max-width: 100%;
 }