The images we use for our infoboxes are created by someone (me for example). The images can be extracted from the game files if experienced with this kind of thing, or obtained by other means. I usually take a blank inventory background tile I made with the blue background, and place the item over it, center it, and make the corner edges transparent. Then the image is uploaded into the database with the preferred Data ID file name, and then can be added into the infobox: "File:Item 3863.png" for example. Infoboxes are best edited in source mode.