We took two pictures with four phones. One picture had a clean lens and the other had a fingerprint smudge on the lens. Check out the results.
This is a picture taken with the Google Pixel XL and a clean lens.
And here's a picture from the Google Pixel XL with a dirty lens. Not much of a difference.
And here's the photo from the iPhone 7 with a dirty lens. There's a very obvious blurry haze.
And here is the photo taken with the Galaxy S8 Plus with a dirty lens. There is a very subtle haze and softness.
And here is the Moto G5 Plus with a dirty lens. Notice there is some haze, but also the camera missed the focus.