Some of you probably already know about this but I thought it might be interesting for anyone who posts pics esp. ones taken with a smart phone. Some of the newer cameras have this as well and it can be handy for remembering where one took a picture, I know there are plenty of times I wish I remembered where I took a pic! Sometimes I even take a pic with my iphone while shooting for just that reason but I never post those online.
If you know about it and remove the data before uploading them then you're safe, but many are not aware the data is there and that it can be easily viewed.