If you don’t have it on your system yet, here is the imagemagick download location. You might also have it in your repository, check your package manager as it might be as simple as calling “sudo apt-get install imagemagick” (on Ubuntu) or “sudo yum install imagemagick” (on Red Hat/CentOs).

Here is a small compilation of command-line tools (by no means a complete list). The list of available commands is actually sheer endless, you’ll be amazed by how powerful this application is.

imagemagick resize

convert image.gif -resize 128×128 resized_image.gif

imagemagick crop

convert  image.gif  -crop 240×360  cropped-image.gif      (add’l params for crop location: 240×360+10+10)

imagemagick rotate

convert image.gif -rotate 90 rotated-image.gif

imagemagick mirror

convert image.gif  -flop mirrored-image.gif

There are many more, actually way too many to list them all here. Have a look at the official ImageMagick usage page for a complete list of image manipulation actions.

Install it using your package manager, most of them should have it in their repository.

sudo apt-get install imagemagick

Once installed, this command will create tumbnails for all JPG’s in the current directory, 200 pixel wide/high on the longest side. Eg. if your image is in landscape layout, it’ll be 200 pixel wide, in portrait format it’ll be 200 pixel high.

for file in *.jpg ; do convert -resize 200 “$file” t”$file”; done

That’s it. Simply change 200 to the size of your liking, or change the extension if your images are in gif, png or any other image format.