Applications on the Mac are really just directory structures containing files, images, assets, executables, and the like. If you've ever right-clicked on an application and selected Show Package Contents, then you know exactly what I mean.
While right-clicking is a reasonable solution for extracting image, font, and other visible assets from an application, the Preview app makes doing so even easier. By simply dragging and dropping an app on the Preview app icon in the dock, you're presented with a easy navigable thumbnail view of all of the app's various assets.