A png or jpg works but the look has to be very special.
normal photos infer 3d by side lighting and color so one side will be lighter and one darker.
To have the engrave come as a relief 3D those hints work against what you want. To do relief carving the high stuff has to be white and as it goes to the back ever darker shades of gray to black. It is also called a bump map when used in such applications as video games.