How so? It's either an actual school regulation or it isn't. If the latter, he's free to shoot. If the former, it's still the rule no matter how big a stink he raises. If the dean is backed by a university reg, he and the school have clout, and the grad student doesn't.
If it becomes an 'issue' and is covered by news, therefore considered 'news worthy', the dean loses the civilian protection he would normally have due to being newsworthy. The landmark case was Sipple v Chronicle Publishing, which followed in the footsteps of Gertz v Welch, which also outlined protections a regular citizin has.
Oliver Sipple was a vietnam vet who saved the life of Gerald Ford by thwarting a would be assassin at a parade in San Francisco. Later, a Bay Area paper (San Francisco Chronicle) exposed Oliver Sipple as a homosexual, against his best wishes. Sipple was known in some circles to be gay, but his family didn't know, nor did those whom he had business dealings with. A result of the article outting him was rejection from his parents and the usual anti-homosexual things you could imagine, leading to him developing an alcohol problem and mental health problems.
He went to court against Chronicle, saying they had no right to publish the story and ruin his life. The courts sided with Chronicle citing that by saving Gerald Ford, Sipple became a hero, and was very much a public figure, and that the story was newsworthy, despite being unrelated to his heroic deeds.
This established the precedent that those involved in something newsworthy lose the protections a normal citizen would have, such as those outlined in Gertz V Welch, in which the courts decided that a civilian does not have to prove actual malice in libel cases to get punitive damages, whereas elected officials and public figures do have to establish actual malice.
Now the cases of this sort are deciding what is newsworthy, which is generally accepted as anything that is being written/talked about and merits coverage. In this case I don't think it would matter, since a Dean of a public university is a public figure to begin with.
I still say ask them to cite exactly what law/statute you're in violation of, as I doubt they know either because they're personally not aware of one (or were told by superiors not to allow pictures) or one doesn't exist. If there is something in regards to your taking pictures in the university library, depending on the scope of the statute you can get around it or fight it. You could always do as Bill said and join yearbook, or just tell them you're on yearbook.