Why when I export unmodified photos from the mac photos app are some heic and some jpeg?

[Bottomsup]

and sometimes i get the same picture in both formats so I have duplicates

 

[barbu]

are any of the photos screenshots or something? Or perhaps they were imported from somewhere else (i.e. photos you received over text and saved to the roll). No idea why you'd have two versions of the same photo though...again, perhaps a result of sharing since HEIC isn't supported everywhere yet.