Use applications like Skype to video chat with your online person of interest. A video chat will allow you to confirm the person you are talking to is real. Keep in mind that some people will still try to be deceitful by wearing facial prosthetics and/or other highly technical masks to portray a different identity. However, a simple video chat will help considerably diminish the possibility that the person you are engaging a relationship with is who they say they are.
Also, remember a video chat may confirm a person's identity but that doesn't mean that what they are divulging is honest information; so do your research.