If the picture has simple lines, the frame probably should also. Remember to let the picture dominate. Let the frame act as a connecting link for the wall and picture. You can get a ready-made frame or select molding and have a frame made. Or you can buy molding and make a frame yourself.
Picture molding is available in a number of sizes and shapes.
Try a variety with the picture. This will help in selection. This holds the picture, backing, and glass. However, builder's molding may be used if a groove is added. This may be cut or made by gluing a thin strip of wood on the back of the molding.