If you are going to say he's negligent for taking the camara into to flightdeck against what the RTS says, then based on that thoery the entire Voyager fleet of pilots are negligent as they all take iPads etc on the flightdeck for use during the flight and the RTS says nothing about them either.
The court passed comment on the deleted photos saying while they don't believe he did it to cover any thing up, they believe he did it to save himself looking unprofessional. It fact he did himself no favours there but ultimately the court believes there was no intent to deceive in doing so.
Considering the Captain admitted negligence some 2 years the MOD need to answer why it took so long to go to court martial. Interestingly according to reports coming out, the judge asked the same question and also was less then happy with the prosecution for the near lack of evidence presented for the 3 charges he was found not guilty of.