For linux(debian or similar)
Step 1: Install ImageMagick
Step 2: "mogrify -path ./where/to/output/ -resize 1000x1000^ -gravity Center -background transparent -extent 600x600 ./where/the/images/at/*"
Step 2 Notes:
- "-background transparent" is to make the image transparent
- "-resize" is the size of the image you want
- "-extent" is the size of crop
- "-gravity" is to make the image center after crop