Those instructions are actually for visa applications, not skilled worker. The head size is different, possibly the rules are different too. The instructions for skilled worker photos are at http://www.cic.gc.ca/english/information/applications/skilled-mission.asp and are specific per visa office although I don't think there is much difference between them. I checked a couple and they said:
The photos must:
• show a full front view of the person’s head and shoulders showing full face centred in the
middle of the photograph;
Full front view of the head would imply that you can not cover your hair but maybe I am wrong. According to http://www.cbc.ca/canada/story/2004/06/25/muslimwomen_040625.html headscarfs are allowed.