Shopify has changed how they store images on stores, images are now stored as WebP Images.
Below is a link to their Changelog where they posted the change on the 17th of July:
If your having a problem viewing them, the following link will add an extension to windows computers to allow them to be easily viewable:
You can also replace any upload fields with a Filestack uploader that would save the file outside of Shopify so it wouldn't be converted. Click here if you want to use Filestack instead!