[css-images] Fix Bikeshed warnings.

Author: tabatkins

css-images/Overview.bs

@@ -14,6 +14,7 @@ Issue Tracking: Tracker http://www.w3.org/Style/CSS/Tracker/products/27
 Previous Version: https://www.w3.org/TR/2012/CR-css3-images-20120417/
 Previous Version: https://www.w3.org/TR/2012/WD-css3-images-20120112/
 Ignored Terms: <offset>, background positioning area, border image area, <meetorslice>, <ending-shape>, Map, center, content
+Ignored Vars: start image, end image
 Link Defaults: css21 (property) display
 </pre>
 
@@ -2110,3 +2111,10 @@ Serialization {#serialization}
 
 		<pre>linear-gradient(red, yellow, black 100px)</pre>
 	</div>
+
+Privacy and Security Considerations {#privsec}
+==============================================
+
+This specification allows rendering of cross-origin images by default,
+which exposes some information of those images programmatically--
+specifically, the intrinsic sizes and resolution of those images.