I mainly use Aperture but this may apply to other software that manages a collection of images. If you use Aperture you will have the option to reference your files or let the application manage them. Always reference, letting the application manage them could (will) cause you problems. If your library corrupts and no longer wants to play the game it could take your images with it. Referencing files leaves them in their purest form and will allow you more options when it comes to accessibility. I started off on the application managed path but thankfully relocating those files is a simple task. Backup, relocate and backup again.