EXIF data: It’s the unsung hero of iPhoneography, and digital photography in general. It’s where location data is stored so you can see your pictures on a map. It remembers when you took that photo, what ISO you used, along with all kinds of other handy data (focal length, flash on or off, even the white balance setting you used).
But on iOS, the EXIF data is mostly hidden from you. But with EXIF-fi, you can not only read it but edit it.
The most common use-case for editing EXIF data is to add your own copyright info, or to add keywords. But you might also want to view the data. For instance, you have two seemingly identical photos in your camera roll, and you know one is a smaller copy of the original. Eyeballing them is inexact. Checking the pixel dimensions is the way to go, or just the image file size in MB. This can be done in EXIF-fi.
The app is free, and will let you read and write everything but the baked-in photo data. And if you pay $1 via in-app purchase you can batch edit images (and enjoy the app ad-free). EXIF-fi might not be the kind of thing you use every day, but at the low, low price of free, it’s certainly worth having around for when you do need it.