After dropping my MacBook, the pictures on it have become pixelated.
You can drop computers or tablets that contain digital files and it is unlikely that these files would be harmed. More likely, the display board or screen has been harmed. You should attempt to transfer these image files to another computer or storage media. Next examine these images on another device. If you succeed with this transfer, I believe the images will then display with the same quality as before.
It is incredibly improbable that physical damage to your computer only seems to affect one type of file (such as images), without causing other noticeable issues (such as general data loss, problems even booting, etc.). I'd go so far as to say it's even statistically impossible.
Now, it's slightly more possible that a certain few files that you might have been working on or editing at the time of the damage are problematic. But even then, you'd probably have more general data corruption problems with those files, rather than just pixelation / lower resolution. Experiencing pixelation would mean the image files and data would somehow have lost information but in a logical, correctly-parseable way. From an entropy standpoint, that just won't happen. The analogy would be to take a random deck of cards, throw it on the ground, and all of the face cards get kicked out and the remaining cards stay in the same order without scattering all over the place. Simply—ain't gonna happen.