https://www.zabbix.com/documentation/2.2/manual/installation/requirements says :
"For other fonts than the default DejaVu, PHP function imagerotate might be required. If it is missing, these fonts might be rendered incorrectly in Monitoring ? Overview header and other locations."

this was changed at some point.
a) it should be figured out which version changed this, and note should reflect this;
b) all locations where this php function could be used should be listed;
c) documentation for all relevant versions should be updated