It's not much, but these images will hopefully be downloaded many times. The
smaller they are, the lowest the latency will be.
Command:
optipng {etherpad_basic.png,etherpad_full_features.png}
BEFORE:
$ du -sch *.png
16K etherpad_basic.png
104K etherpad_full_features.png
120K total
AFTER:
$ du -sch *.png
12K etherpad_basic.png
92K etherpad_full_features.png
104K total