ImageMagick is probably the best (free) image editing library around. I've used it in Windows, indirectly via ColdFusion, and php! 'Tis everywhere. Anyway, some links:
Some excellent advanced examples of using ImageMagick with before and after pictures:
http://www.cit.gu.edu.au/~anthony/graphics/imagick6/
Convert all Apple HEIC format files to JPEG in bulk:
magick mogrify -format jpg *.HEIC
Tags: Image, Magic, Magick, ImageMagic, ImageMagick, graphics, images, command line, tool