If you’ve never tried doing a search in your Mac or iOS photo library, check out this post for Mac and this post for iOS. There are some searches you can do without any prep work on your part (search for “cat” or “water”), but some searches do require some effort on your part (search for a particular person, for example).

I do wish there was a way to run a search on all images on my device, rather than just the images that have been imported into Photos. I suspect that eventually, images on our devices will all be tagged in some way, all backed up, and all searchable, whether we created them or not.