Photos for OS X and iOS let you sync your library to iCloud, so that you can have thousands of photos at your beck and call without having to store them locally on your machine or device. But what about when you don't have Wi-Fi or cellular data readily accessible?

Never fear: Whether you're stuck on a plane, in a tunnel, or simply want to show off photos when you don't have internet access, here's how you can still view and manage your iCloud Photo Library images.

Option 1: Download everything

If you happen to be toting around a particularly large-capacity iPhone, iPad, or Mac, your simplest option is to turn on the "Download and Keep Originals" setting. This will pull every image and video you've stored in iCloud Photo Library down to your device, where it lives until you decide otherwise.

This, however, isn't always the best option: Unless you have a 128GB iPhone or iPad — and honestly, even if you do — your full library may take up quite a large portion of your drive, and you can't delete images to free up space lest you also want them deleted anywhere else you use iCloud Photo Library.

Option 2: If you want full-resolution photos and editing abilities, download certain things before you go offline

Prefer to use iCloud Photo Library's Optimize iPhone Storage setting? That's fine: You can still download high-resolution copies of your photos for viewing or editing while offline.

First, a quick primer on the "Optimize iPhone Storage" setting: This appropriates a percentage of your free space for photo storage; this percentage fluctuates depending on how much of your storage space you've taken up with other content, as well. For instance, if you have 5GB of apps on a 64GB iPhone, iCloud might allot 20GB of space to storing Photos, leaving 30GB or so (after operating system space) for other items. If you have 15GB of apps, iCloud's photo allotment might be closer to 10GB.

As your storage ratios change, iCloud Photo Library removes local copies of older photos using semi-intelligent rules (older images, those you haven't viewed in awhile, etc) to free up more space.

So, while you can technically download an image from iCloud Photo Library by tapping on it — you'll see a processing icon in the lower right corner of the photo as it downloads — there's no guarantee that image will stay downloaded to your iPhone forever, especially if you don't look at it for awhile.

Instead, to make sure that you have the right high-res downloaded images on your phone, tap to download them before you know you'll be offline.

Option 3: If you don't need to edit or see full-res photos, iCloud's got you covered!

If you just want to show a friend a ridiculous photo from a past vacation, or you're bored while on an airplane and want to delete some old photos, you don't actually have to have internet access.

You see, iCloud Photo Library stores small low-resolution thumbnails of all your images, whether or not their full-resolution versions are on your device. It also caches and queues any changes you make to your library while you're offline.

In plain speak, this means you can view any of your undownloaded iCloud Photo Library images while offline — you just can't view them at high-resolution, edit them, or share them. You can, however, add them to albums or delete unwanted photos. (I personally tested this during an airplane ride and managed to cull quite a few duplicates and other poorly-shot photos from my library.)

iCloud Photo Library: The Ultimate Guide