Assuming you’re in folder a the following might work for you find . -name “*.jpg” -exec mogrify -format png {} \; You can use the find command to get all the jpg files in all the subfolders and pass your command as an argument to find
After another half hour of searching I have stumbled upon the overly simple answer. The following will resize an image with the exact dimensions given: mogrify input.png -resize 256×256! output.png If you want to read more about it, I got the answer from this link: https://superuser.com/questions/212752/how-to-stretch-an-image-in-one-dimension
“Mogrify” should be called from the directory with the original thumbnails, while the -path parameter is for pointing target directory. mkdir public_html/images/new-thumbs cd public_html/images/thumbs magick mogrify -resize 16×12 -quality 100 -path ../new-thumbs *.jpg http://www.imagemagick.org/Usage/basics/#mogrify The last arguments are the list of files, so you can filter by name 1-*.jpg for example.