Thanks for taking the time to post. Sorry to hear you've been charged for five picture messages you haven't sent. I appreciate it can be a shock when this happens.
As AlexKid mentioned, it doesn't have to be a picture as such. They could also be a text message which was sent to an email address. This happens if your contact has an address assigned to them.
I'm afraid nothing can be done regarding the charges if the text messages were genuine. If you feel they are not genuine then please call the team on 789 from a Virgin Mobile or 0345 6000 789 from any other phone.