Dear Rich Staff has worked as a reviewer and sometimes we feel funny panning somebody's work even if we didn't have to ask permission for anything. That's because we know how much effort went into the thing and we feel bad deflating the tires, so to speak. On the other hand, everybody's a reviewer these days so maybe reviews really don't matter any more.
Right, you had a question. Obviously your chances of obtaining permission are reduced if you inform the person from whom you're seeking permission that you intend to pan the artwork. So, our suggestion would be not to mention it. Like Admiral Hopper used to say, "It's easier to ask for forgiveness than it is to get permission." Though some may disagree with that approach, we feel it's fine in this situation. After all, academic criticism is valuable and is intended to provide benefits to the artist and the public. So, we see nothing wrong with simply stating that you are preparing an academic essay and need a high quality reproduction of the work for reproduction with your essay. If you cannot get permission and you are going to produce a printed publication, you may be able to reproduce thumbnails under fair use principles -- at least that's been the trend recently for books and websites. And of course, though it may be expensive, some artwork can be licensed with few questions asked through sources such as VAGA and ARSNY. (Columbia University has a site explaining the licensing principles of museums and galleries.) And while you're at it, we're curious what you think of this artwork?