Saccade uses ARKit face tracking to measure which image you actually look at longer in a side-by-side (well, top-and-bottom as it runs in portrait mode) comparison.

Import a set of images, and it runs every possible pair, tracking your gaze for a dynamically-timed duration each (typically just a fraction of a second). It then ranks the images in descending order of how long your gaze lingered on each. You can then rerun the same batch of images to compound data over multiple tests, or start new. And of course you can easily share your results with friends and colleagues.

Bonus: The Emoji Duel game is pretty fun for onboarding; our 4yo can't get enough of it. :)

100% free, no backend, no user auth, no data leaves your phone. Requires iPhone with Face ID.