A practical check for believable photo enhancement
An enlarged image can look sharper at first glance and still lose the texture that made the original believable. I compare the source and result at the same scale before judging the improvement.
First I inspect high-contrast edges for halos or double contours. Then I check flat backgrounds and shadows for waxy denoising. Text, hair, eyelashes, and fabric are useful stress tests because invented detail becomes obvious there.
Portrait restoration needs extra caution: a cleaner face is not automatically a more faithful face. Identity, expression, and small asymmetries should remain stable.
Disclosure: I work on PhotoEnhancer. I use its live before-and-after workflow at https://photoenhancer.dev/ when testing these checks.