Checking the site with the PageSpeed extension, one of the reports was
in reducing image size. This reduced the number of bytes by 67%.
It was done with optipng -o7 -fix *.png in the app/assets/images dir.
References:
optipng: http://optipng.sourceforge.net/
PageSpeed extension: https://developers.google.com/speed/docs/insights/using_chrome
