it is still not possible to save images in HEIF format on OS X. Bugs are open since months but it seems that Apple won‘t support this feature in the near future. Are there any available libraries which can be used as a workaround. Otherwise I think HEIF will be the next dead horse on the road...
Still no support for saving HEIC/HEIF
As there is no concrete workaround to solve HEIC's limited compatibility issue, we can only ask heic viewer for help. In current market, it can do well in converting heic images to other format, like JPG, GIF, PNG, BMP, etc. To avoid your iPhone saving images in the form of HEIC, you should go to camera settings to select "Most Compatible" as your output format. Anyway, I have no other way to go but draw help from such a handy heic converter program.