Part of my job is to take pictures of our product before we ship it out. This particular picture is of the inside of an FRP storage tank. Of course, I work in a very dusty environment. When the flash goes off, it sometimes catches images of out of focus dust particles. That's what the blurry circles are. However, some people who fancy themselves as ghost hunters say that these "orbs" are actually the souls of the dear departed. They often blow up the pictures of "orbs" saying that faces can be seen in them. I've enlarged two of the orbs in my picture. What do you think? I still think it's just dust particles.
The original photo is too big to put on the blog. Download the big picture.
Here's a nice orb.
And the brightest one in the picture.
Commenter Eshu has an excellent article on orbs on his blog.