You can make any item transparent, but to do so you will have to map the UVMAP and process the item's RVMAT. The UVMAP is responsible for each part of the item's image mapping, while the RVMAT processes the colors, brightness, and so on.
An easy way to do this is to open the texture's PNG, find the place where the viewfinder is located, and simply remove it or make it almost transparent. When you upload your texture to the game, it will also become transparent, as you did in Photoshop.