Hydra is a photo app available in the App Store that, among other things, allows you to take high resolution (up-to 32MB) photos with your iPhone. Here are some samples comparing the native Camera app in iOS12.1 on an iPhone 7+ with the “HI-RES” option in Hydra. Be sure to click on the photos to open full size and take note of the lettering on windows, signs, etc to better see the difference in quality.
Sample 1 Zoomed
You can see from the images above that the Hydra app, using the HI-RES option, adds a lot of nice detail. The images are also larger, higher quality. For example, the latter image with the native Camera app is 4032 x 3024 (2.8MB) where as the version taken with the Hydra is 6528 x 4896 (4.2MB). The Hydra app costs $4.99 (no in-app purchases).