I've made dozens of picture frames over the years and for me it depends on the size of the frames, the quantity needed, and the types of wood. For smaller frames, as Jerry suggested glue and pin nail does the trick-especially when doing a large quantity so that clamping is not require. V -nails would work as well but then you need to clamp them while using a special tool and fasteners and are difficult to use in harder woods unless you have special equipment. For larger frames I would biscuit and/or spline the joints. Just my 2 cents...