Hi, I know that flickr has this "picture sharing security system" but there are pictures which I guess can be shared (downloaded) but what if under the picture there is a mark for copyright ?
All photographs are automatically copyrighted. Some people allow you to use their images under certain circumstances and conditions - it depends on the actual usage terms of the specific image. If someone uploaded a picture to facebook that didn't belong to them, you are still liable to the original copyright holder.
If you want to find Flickr images to use, go to their advanced search page, tick the box that says "Only search within Creative Commons-licensed content" AND tick the box that says "Find content to use commercially" That will only turn up images where the photographer has explicitly licensed the photo for use by others.
You are still possibly at risk. There was that case from a couple years ago where Virgin Mobile used a Flickr photo in one of their ads. http://www.out-law.com/page-8494 That was thrown out though since the lawsuit was in the US and the ad appeared in Australia.
Interesting. It sounds as if at the least Virgin was breaching the license agreement because they didn't give attribution. There are also additional rules if you use images with people in them - you are supposed to get a model release. Stock photo sites like iStockPhoto do that for you. Flickr does not. It's best to contact the photographer to get explicit permission for photo use.
They gave attribution to the Flickr account of the photographer, which was in compliance with the attribution license he was offering it under. I can't find the photo where you can see it, but it's in the bottom corner... http://farm1.static.flickr.com/219/515961023_dd279b3fc0.jpg IMO the girl's family was just out for some money. I don't know what the laws are in Australia where she was when it was taken, but in the US model releases aren't necessary for photos taken in public places. This would have been unpaid modeling work anyway (or close to it) since the license would have been worth so little on a photo like this. It was thrown out of US court due to a lack of jurisdiction. I would have liked to have seen the outcome as a test to these Creative Commons licenses.