Wallpaper would not be able to cover wall imperfection or existing conditions. They are always the reflection of your wall condition; Any bumps/uneven/moulding issues will still appear on the wallpaper after installation.
However, for minor uneven wall surfaces, you may consider using wall coverings of thicker ounces such as vinyl wall covering or the natural speciality ranges to conceal them. Alternatively, you may also consider other wall options, such as Kastone Bricks, to cover wall imperfections.