call thumbnails, not original images. Slight CSS improvement.

git-svn-id: https://plugins.svn.wordpress.org/last-seen-posts-widget/trunk@811077 b8457f37-d9ea-0310-8a92-e5e31aec5664
stable tag

git-svn-id: https://plugins.svn.wordpress.org/last-seen-posts-widget/trunk@811080 b8457f37-d9ea-0310-8a92-e5e31aec5664