Notact, that looks like a spline down the mitered edge, is that correct?
I just use the old weak butt joint. Just run the ends that hold frames down the table saw and put those boards in between the longer ones. Glue, screw and liquid nail end grain and then paint 3 coats.
For me, box joints and dovetails waste wood as 1 1/2" of board are cut into. I use joints like those for the pieces I want to look nice. I know, I know, it is weaker but for setup time and waste, not to mention the waste when using (scrap) for trial fits. Just faster, especially when it seems my to do list never ends.