Door Jamb Strike Plate x 2

-Remove striker plate.
-Cut a piece of wood the right thickness and size to fill the old striker plate hole. Glue it in and let it set for a day or two.
-Look at the 'new' striker plate, it doesn't really look right. It looks too far to the left, but if the door closes properly and it matches the door hardware, okay. Trace around the new striker plate with a pencil and then cut away the wood so it is properly recessed. Trim the new striker plate hole so it doesn't look like it was made with an ice axe.
-Fill and smooth over the whole thing except the new recess with filler; sand, paint.
-Screw the new striker plate on.

Forget the hassle of making inserts. Just get a quart of wood epoxy filler. Remove the plate, clean the area, mix a batch of filler and fill the area. Once it's cured shape and sand.

http://www.jbweld.com/products/premium-epoxy-putty-kit

both methods work , be it a dutchman patch or using epoxy or autobody fill,. for a dutchman patch you need to either router or chisel out at least 1/4" deep section and patch back in... with filler it can require several passes to fill larger voids then quite a bit of sanding. if you put it on too heavy it can take forever to dry at the deepest points so i apply it in thin amounts to speed up drying time