IE8 doesn't need help with responsive images, they work just dandy apparently (see http://jsbin.com/idesit/1)

docs/assets/css/bootstrap.css

@@ -322,7 +322,6 @@ a:focus {
 }
 
 img {
-  width: auto\9;
   height: auto;
   max-width: 100%;
   vertical-align: middle;
@@ -1226,12 +1225,6 @@ label {
   font-weight: bold;
 }
 
-input[type="search"] {
-  -webkit-box-sizing: border-box;
-     -moz-box-sizing: border-box;
-          box-sizing: border-box;
-}
-
 select,
 textarea,
 input[type="text"],
@@ -1282,6 +1275,12 @@ input[type="checkbox"] {
   width: auto;
 }
 
+input[type="search"] {
+  -webkit-box-sizing: border-box;
+     -moz-box-sizing: border-box;
+          box-sizing: border-box;
+}
+
 textarea {
   height: auto;
 }

less/scaffolding.less

@@ -71,7 +71,6 @@ a:focus {
 img {
   // Responsive images (ensure images don't scale beyond their parents)
   max-width: 100%; // Part 1: Set a maxium relative to the parent
-  width: auto\9; // IE8 need help adjusting responsive images
   height: auto; // Part 2: Scale the height according to the width, otherwise you get stretching
 
   // Match vertical alignment with other comment elements