Next comes the stain. Stain stinks. I would highly recommend that you take it to a well ventilated area. If you are using oil based stain, make sure to take precaution to protect your skin and surfaces.
Lightly rub the stain over the exposed wood. Use more to achieve a darker appearance, less for a lighter appearance. Once it is dry, you can apply a clear coat to finish the look.
And voila! One distressed picture frame. I will caution you that if you are working with a light paint, you will want to work in small areas using the stain sparingly. While excess stain does not show up on the black paint, it will show up on lighter ones.
So there you go. Distress away and enjoy the end result, remember it's distressed so you don't need it to be perfect!