Can you turn on .htaccess browser caching for results.
#Caching ExpiresActive on ExpiresByType image/gif "access plus 1 year"
Other performance enhancing things you can do are: Set specific size for the images, inline or via CSS. CSS would be easier. This would speed up the page loading and be also less annoying while all the requests are going through (having default sized images deforming the table before they load). Minify the HTML/CSS/JS (less to send).
Not doing/doable for known reasons: Serve identical files from the same url. (flag images)