Index: wp-content/themes/twentyten/style.css
===================================================================
--- wp-content/themes/twentyten/style.css	(revision 23123)
+++ wp-content/themes/twentyten/style.css	(working copy)
@@ -832,6 +832,7 @@
 }
 .wp-caption img {
 	margin: 5px 5px 0;
+	max-width: 622px; /* caption width - 10px */
 }
 .wp-caption p.wp-caption-text {
 	color: #888;