Hi, it sounds like what you have is an orb photo. The theory on orbs is that they are a ball of energy Which "could" mean the presence of a spirit. There are also other things that could cause a false positive orb photo like dust, bugs, reflection things of that sort. Without seeing the photo I could not say for sure.
If you are interested in knowing more about them here are a few links that can explain more about orbs and how to get a better idea of wether it's a true orb or a false positive.
You can also e-mail the photo to [email protected]
and I'll have a few of us take a look and let you know what we think.