How many photos do you have in your phone? Hundreds? Thousands, even? I bet you'd hate to lose them. And yet phones get lost, stolen and broken every day. Are you playing it safe?
Apple's iCloud affords a backup of sorts, but doesn't really give you a way to access your photos via anything except other iDevices. (You can't sign into iCloud.com, for example, to view and manage your photos.) What's more, if you delete some photos from your iPhone in order to free up storage, those photos get deleted from your iCloud account as well. (That's because your "backup" is really just synchronization.)
Wait, so iCloud doesn't technically back up your photo library? According to Apple's overview page: "If you turn on iCloud Photo Library, your photos and videos are already stored in iCloud, so they aren't included in your iCloud backup." I'm pretty adept at all things iPhone, but the vagaries of iCloud? Umm...
Update: I goofed. Apple recently added Photo Library to iCloud.com, so you can indeed manage your photos that way. But your free storage is capped at 5GB, and I still find it unclear whether this is straight-up synchronization -- meaning anything deleted from your device is deleted from iCloud as well -- or a more traditional backup.
Update No. 2 (9/18/15): I received a few clarifications from an Apple rep, including this one: "After you enable iCloud Photo Library, your photos and videos are automatically uploaded and stored in iCloud. They won't be duplicated in your iCloud backup because we don't want to duplicate the storage." Also, with regard to freeing up storage: "If you turn on Optimize Storage, iCloud Photo Library will automatically manage the size of your library on your device, so you can make the most of your device's storage and access more photos. All of your original, full-resolution photos and videos are stored in iCloud while device-size versions are kept on your device. You can download the original photos and videos over Wi-Fi or cellular when you need them."
There are still aspects of iCloud backup -- especially with regard to photos -- I find confusing, but once you get past the learning curve, the need for a third-party alternative seems less.
Plan B (for 'Better')
Fortunately, there's a far less vague way to back up your iPhone photos: Use a different cloud service. This not only helps you free up storage, but also gives you better tools for managing the photos you've backed up.
For purposes of this tutorial, I'm going to focus on Google Drive and Microsoft OneDrive. Both services offer 15GB of free storage, cheap upgrade options and, most important of all, iOS apps that can automatically archive your photo library.
Other services, including Box, Dropbox, IDrive and SugarSync, can do likewise, and if you're already using one of them, there's every reason to enlist them for photo-backup duty. But these guys offer less free storage up front and costlier plans if you need more. So if you're just getting started down this road, I recommend Google Drive or OneDrive.
I'll wager you already have an account with one or both (and if you have an Office 365 subscription, you actually have a lot more than just 15GB at your disposal), so all that's left is to install the corresponding app. Here's Google Photos for iOS (the Google Drive app pales in comparison when it comes to photo backups) and Microsoft OneDrive for iOS.
The first time you run either app, you'll need to sign into your account. In the case of Google Photos, you should then see a pop-up offering to back up all your photos and videos. As shown in the screenshot below, you can also choose whether this happens over Wi-Fi only (recommended) or, if you have a generous data plan, Wi-Fi and cellular. (Choose the latter only after your initial backup -- which is likely to be sizable -- is complete. It might be worthwhile if you're traveling and want your vacation photos backed up on the go.)
Next, the app will ask if you want "high-quality" backups and free, unlimited storage for them, or full-resolution originals that count against your available storage. Not sure which option to choose? Here's a tip: Because your iPhone's camera snaps photos that are under 16 megapixels, the "high-quality" option will "essentially look the same" as your originals, according to Google.
In OneDrive, you'll need to tap the Photos icon, then enable the Camera Upload option (by tapping Turn On) and approve access to your photo library. (You may also want to allow notifications so you can get updates on backup progress.)
The Google Photos app is a bit frustrating because after you enable photo backup, it provides no indication it's actually doing anything. To make sure it is, tap the Menu icon, then Assistant; you should see a progress meter.
By default, OneDrive will also limit itself to Wi-Fi for photo uploads, but if you want to allow it to use cellular as well, venture into the settings, tap Camera Upload, and then toggle Use Mobile Network.
Microsoft's app wisely relies on a badge that shows how many photos it has left to upload.
The only real hassle in all this is that both apps will pause their background backups after a period of inactivity, so for your initial backup (the big one), you'll want to leave your iPhone plugged in and awake, with the app running. (You may need to temporarily tweak the power settings to keep it from going to sleep.)
One key thing to remember is that these apps are essentially making copies of all your photos, then syncing them to your cloud account. That's why it's safe to delete photos from your iPhone after the backup is complete. However, if you delete a photo from within Google Photos or OneDrive, it will be permanently deleted from that service. (Actually, I think Google still keeps them in a virtual trash bin for a couple weeks.)
Also, if you ever end up replacing your phone, due to either a loss/breakage or an upgrade, your cloud backup won't automatically restore the photos to the new device. They'll still be accessible, of course, but only via their respective apps (and your PC, of course). It's not like a traditional backup restoration where everything gets returned to your iOS photo library.
Make sense? No doubt about it, this can get confusing. But now you should have the tools you need to at least start making a free backup of your photo library, after which you can delete photos you no longer want consuming your phone's storage.
Have you found a better, easier and/or cheaper way to go? Explain it in the comments!