I'm currently writing my master thesis and would like an opinion on whether or not to use a cover illustration on the thesis.
I've noticed many students around me do not take the time to make the cover page attractive (e.g. a simple title is all).
What is the "standard" convention regarding the cover page of a master thesis?
Note that I have no restrictions from my university.
The primary reason for not having a "pretty cover" is simple: practicality.
Keep in mind that many schools will have "official" copies of the thesis bound; for archival purposes, and to keep production costs down, the covers don't typically have illustrations, but are usually monochromatic standard bindings. The cover art would therefore not be obvious to anybody looking at the thesis—and the low traffic for theses means it's usually not worth the effort to produce it.
However, as Chris points out, if your school doesn't have a policy, you can do what you'd like. On the other hand, I'd focus on the quality of the material presented in the thesis before worrying about the cover art!
I'd like to provide a counter to the "content is what matters" advice. Of course the content is what it's all about, but I think that a great many people in academia underestimate the importance of presentation.
Look at the way people decide whether or not to read a paper. They look at the title. If that suggests that it's interesting to them, they read the abstract. If that's interesting enough they read the introduction and maybe the conclusion, and so on. That means that of the 4000 or so words in the paper, the five that make up the title are the most important. You're fully justified in spending as much time on the title as on 1000 words of the description of your method. The presentation of your paper is not just gloss, it determines the size of your audience. If your presentation is bad, your results have to be really exceptional to find even a small readership.
This translates directly to your Master's thesis. A nice cover shows that you care. What's more, the largest group of people that will come into contact with it, will only pick it up, look at it and put it back down again, without even really reading the title. Your cover illustration is the only opportunity you have of communicating with them and enticing them to read the title properly. From that, the summary, and from that the first paragraph of your introduction and so on.
Don't mistake presentation for gloss. Academia is all about communication, and communication is worrying about the details.
It's your thesis, and if your committee approves it with beautiful cover art, then you're all set.
For professional theses, the standard is a plain cover with pertinent details about the thesis. Departments or universities generally have a template document or provide specific guidance, but if that isn't true for your school, then I wouldn't worry about it.
Bottom line: I would discuss it with your advisor, and other committee members. If you want it to be a surprise to them (not advisable), then by all means give it a shot.
For many students, there are strict guidelines that describe how a thesis can be formatted. If you're not restricted by guidelines, and if you have the time and inclination to have your thesis be a beautiful object, there's no reason not to.
Although the content matters much more than any amount of fancy layout, great presentation can make a difference. As in food, the first bite is always with the eye.
