Frame, or not
The question can be answered with a clear yes.
Of course you could nail an oil painting without frame on the wall, or glue. But, ugh, how it looks like! This could perhaps to do with an art print poster in a dorm room, but not with something more valuable oil painting reproduction in your living room!
So quite clearly, a framework must be!
The next question to answer is no longer so simple, namely, whether or not we could do without the expensive jewelry frame.
This is also a matter of taste. Especially modern paintings do quite well, even if they are just curious on a stretcher. Since there are also extra strong stretcher and all our images have a painted edge, then so are the edges of the image Stretcher a continuation of the image.
The answer to the next question to answer is again very clearly, namely, if you also need a stretcher when an oil painting is mounted in a picture frame. The answer is clearly yes!
The oil painting must first be stretched on a wooden frame, and is then mounted it in a decorative frame.
So if I could relieve you of the decision, which unfortunately I can not, I would present the image in any case in a frame!