This isn’t a sweeping deck designs, but here is how I do the deck picture designs. Lay out the design on deck and cut it out. I file about a 5 degree taper on the edges. Then put tracing paper over the individual hole part and using the edge of a pencil do a pencil rubbing of the edge of the hole on the tracing. Cut the tracing paper shape out with scissors, spray the back with adhesive and stick it to your wood strip. Cut this wood out to the tracing pattern edge with approximately 5 degree taper leaving it slightly big. Then start chalking the hole edge with blue chalk and fitting (filing & sanding) the wood piece on the chalked area. It takes awhile but you can get an exact fit.

John