"But you didn't have a copyright on it!"
A sentence said to me recently by a boy who took a picture that I had taken off Facebook and re-posted it on his own Facebook.
"Um, yes," I replied. "They are still in fact MY photos that I took with MY camera."
He didn't seem to understand.
Here you will find some useful information if you are questioning whether or not it is legal to use a photograph you are taking off the computer. The simple answer: No.
If it does not belong to you, it is not yours. If you take it, you are stealing. A simple, moral idea that is often betrayed. Copyright laws protect an artist's work. Writers need to protect their words; photographers need to protect their images. The laws may appear to be complex, but the rules are basic.
This is all you need to know. It's mine. Don't take it unless I've given you permission. If it's on Facebook and I've tagged you in it, then consider that permission. If my watermark is on the photo, then I ask you to not crop it out when making one of my photos a profile picture.