How to find all images with a certain pixel size using command line?

You can use identify from imagemagick, and you can use the following command:

find . -iname "*.jpg" -type f -exec identify -format '%w %h %i' '{}' \; | awk '$1<300 || $2<300'

the use of -exec <command> '{}' \; makes sure that your filename can have spaces in them, alternatively you can use

find . -iname "*.jpg" -type f | xargs -I{} identify -format '%w %h %i' {} | awk '$1<300 || $2<300'

where the -I{} takes care of the same thing.

What I like about identify is that you can specify the output format; in this case '%w %h %i' which gives the width, height and full pathname of the image. Then the awk expression only keeps those lines for which the image is smaller than the desired size.

Example of the output:

64 64 ./thumbsup.jpg
100 150 ./photomin.jpg

Edit: If you want the filenames only (for piping to rm for instance), simply change $line in the awk statement to $3, then it will only print the third column.