How thick are your acrylic pieces? Do you intend to use each piece separately, or are you engraving one piece and still intend to use the 2 pieces as a frame for a traditional photo?
The most important part of this project will be to prepare your photo. There are quite a few posts in the forum regarding this, so I think your best bet would be to read everything you can about photo prep. Here is a place to start: Acrylic engravings of feminist icons