Mike's solution will just show the image, but any title set on the button will not be visible, because you can either set the title or the image.
If you want to set both (your image and title) use the following code:
btnImage = [UIImage imageNamed:@"image.png"];
[btnTwo setBackgroundImage:btnImage forState:UIControlStateNormal];
[btnTwo setTitle:@"Title" forState:UIControlStateNormal];