To be your own it would have to be substantively different from the original source material. For instance, I could paint an interpretation of someone else's painting that was quite different from the original and consider that my own creation, but I couldn't paint a duplicate that looked exactly the same and call it my own.
In your case, if you are just compositing or collaging the pictures together than you would not be substantively transforming the original work so you would need to attribute sources and make sure you have the right to use the images and make derivative changes to them.
If what you are doing involves some sort of creative transformation than it is possible the resulting image would be your own. It depends on the level of transformation. There really aren't very clear boundary lines when it comes to this issue. Either way, it never hurts to give attribution to the original work.
As MickS says, copyright is a complex issue. It also varies by country. My answer is a non-professional opinion based on American law.
You also shouldn't use faces of celebrities for your profile picture.