NSW Photograpy Rights and Legal Issues
This is from Andrew Nemeth's site at http://4020.net/ - specifically http://photorights.4020.net/
This is applicable to cosplay photography 
If you're uncomfortable, bloody well express your concerns to the photographer!
Summary:
- It is perfectly legal to take photos of people without their consent
- This applies so long as you're on public land
- Even if the subject is on private property, eg. sniping into their backyard with a 300mm lens
You do need consent if the person has a "reasonable expectation of privacy"
- There's a little more than this, but that's the gist
- Publishing photos (eg. putting them on the interwebs) is legal, so long as they're:
- Not defamatory
- Not indecent, offensive, or otherwise demeaning
- Not being used for a commercial purpose
- "Commercial use" doesn't mean selling the photo, it means using the photo to sell stuff