EDIT: themumu: Maybe I'm just old fashioned, but how hard is it to just ask first?
My photos contain the line Copyright DShearon 2013 All Rights Reserved. That means it's mine unless you ask. Posting doesn't make it free to take.
Dale
It may not be hard in any single case, but over the course of time an interested person spends looking at cool photos, it can become tedious. For example, when I first got a computer with an internet connection, I got into a full on hoard mode. I would scout photography and arts websites, such as deviantART, and a load of others and save stuff I liked onto my hard disk. If I were to attempt to contact every single person whose images I saved (mainly for wallpaper use, but sometimes just for staring), I would not have any time to do homework and would surely have flanked several courses at school
For me internet is like a river with a ferocious rapid flow - you cannot tame it, you cannot set your own rules in it, you have to be very aware of the risks and dangers as you get in, and in exchange you can become part of that flow and perhaps fish out the experiences you seek. Every single thing I post, I remind myself that I better be ready to stand on a podium in front of a crowd and shout it, while the crowd takes photos and videos of my doing it. Once you let your words, images, everything out - you cannot control them and cannot take them back. It's just the way this river flows, it's physics.
As for the copyright clause, you should check the fair use exemption.