Command Line to Convert Images for Stickers

The following tutorial is for macOS

brew update && brew install imagemagick

to your folder for the candidate images for stickers

convert all jpg & jpeg to png

magick mogrify -format png *.jpg
magick mogrify -format png *.jpeg

for all the pngs, resize to be within 512x512

magick mogrify -resize 512x512 *.png

Afterwards, this folder of images meet the requirements for telegram stickers