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How well does photo storage to cloud work?
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That question does bring up a significant aspect when it comes to Android vs. iPhone. With your iPhone you have a backup/restore/migrate solution that's already implemented with your device. Everything gets uploaded into your online iCloud account where if needed you just restore your phone if some problem does occur, and/or you can easily just migrate your old iPhone's user set up onto a new iPhone. With Android however, we're stuck with setting up our own backup solutions, and in the event we need to migrate from an old phone to a new one, there may or may not be easy solutions to do this successfully. (i.e. If you do opt to get a Samsung, you can use Samsung's Smart Switch utility to do full backups and restores, and migrate from one phone to another which works out better if both are supported Samsung phones. But the process is still not as seamless and thorough as iCloud. (This does highlight a notable difference between the two platforms, where Apple has almost complete control over its hardware and software, along with fundamental services, while Android is much more diverse with Google only having control over the Android OS and numerous manufacturers, carriers, and retailers inserting themselves into a less structured environment.) Also keep in mind not all the different brands of Android phones have similar backup/restore/migrate services. There are several third-party utilities in the Play Store that are developed independently that are worth looking into, but that will be matter of always doing a little research on any app you install on your own to validate its credibility and actual functionality. Google does screen out a lot of crapware from its Play Store on a continuous basis, just as Apple does in its online Apple Store, but not everything submitted by the miscreants can be found and revealed immediately so just be a little cautious about what you do install on your own.
But getting back to your query regarding online photo storage, there are well established services that work quite well. The Google Photos app is a popular choice, it's basically a photo manager app up front, but it's ability to do backups and syncing of your photo library up into your online Google account in the background is a big plus. This gives you the ability to always be able to access your photo library from either your phone or using a web interface on any web browser. If you're wary of handing too much of your data to Google, there are of course apps for other third party file sharing services like Dropbox, SpiderOak (a privacy focused service), OneDrive, etc. If you're an Amazon Prime subscriber, the online Amazon Drive is included at no extra charge (up to 5GBs).
Oh and regarding your wife amassing lots of photos, if she's just using the free, default iCloud storage capacity of 5GBs, with Android, the free, default is 15GBs.