Today, a colleague of mine uploaded a large number of images, only to realise later that they were all uncompressed and the site was loading noticeably slower.

His first thought was to compress them and re-upload everything again—but why do something redundant when you can handle it easily from the terminal using ImageMagick?

Previously, I’ve written about how ImageMagick makes it easy to resize images in bulk. However, sometimes you don’t want to touch every image in a directory.

In cases like this, if you already know which images need resizing, you can list their filenames in a text file and let ImageMagick process only those.

Assume a files.txt like this:

image1.jpg
photo_02.png
banner.jpeg

You can then resize just those images while keeping the original aspect ratio intact and avoiding upscaling:

while IFS= read -r file; do
  [ -f "$file" ] && mogrify -resize 500x600\> "$file"
done < files.txt

This works well when cleaning up large media folders or fixing legacy content where only a subset of images needs adjustment.

Hope you found this tip useful!