If it doesn't have a copyright notice, it's not copyrighted
This was true in the past, but today almost all major nations follow the Berne copyright convention. For example, in the USA, almost everything created privately and originally after April 1, 1989 is copyrighted and protected whether it has a notice or not. The default you should assume for other people's works is that they are copyrighted and may not be copied unless you know otherwise. There are some old works that lost protection without notice, but frankly you should not risk it unless you know for sure.
It is true that a notice strengthens the protection, by warning people, and by allowing one to get more and different damages, but it is not necessary. If it looks copyrighted, you should assume it is. This applies to pictures, too. You may not scan pictures from magazines and post them to the net, and if you come upon something unknown, you shouldn't post that either.
The correct form for a notice is:
"Copyright [dates] by [author/owner]"
You can use C in a circle © instead of "Copyright" but "(C)" has never been given legal force. The phrase "All Rights Reserved" used to be required in some nations but is now not legally needed most places. In some countries it may help preserve some of the "moral rights."