Measure the sides of the painting along the edges. Add the length of each of the four sides together. This is the length of the lattice you will purchase.
Measure the depth of the painting. The lattice will be nailed flat to the sides of the canvas, so you will need to purchase lattice that is wide enough to cover the depth of the painting. If the lattice is wider than the sides of the painting itself, this is alright. In fact, it may be preferable, since it will give the painting a more noticeable presence on the wall.
Purchase high-quality straight-edged lattice from a lumber yard.
Use a saw to cut the lattice down to match the sides of the painting. For the top and bottom of the painting, measure enough lattice to cover the right and left sides once the lattice is attached.
With a paint brush, stain the lattice to the appropriate color. The stain is chosen on a case-by-case basis. Some paintings are best complemented by a dark stain, others by a lighter stain. Some stains are more red, some are more brown or black, and some are more blond. Really, it is your taste that determines what you will choose. Maybe you want the frame to blend into the painting--therefore, choose something as dark or light as the painting itself, and of a complementary hue. If you want the frame to accent the painting, choose a color and hue that stands in contrast to the painting.
Allow the stain to dry.
Hammer the lattice intended for the right side of the painting into the right side of the canvas. The lattice should be laid flush against the sides and nailed flat. Use small nails with tiny heads, so as to be discreet as possible.
Repeat the above step for the left side. Then repeat for the top and bottom.
Turn the painting over and face the back of the canvas. Screw an eye hook into the inside of the stretcher bar on the left, then another one into the stretcher on the right.
Tie the end of a length of picture wire into one eye hook, then the other end of wire to the other eye hook. The wire should be slightly longer than the length of the painting from one side to the other. Your picture is now ready to be hung.