The exiftool command line tool, which is free and open source software which available for Mac (as well as Linux and Windows), can easily identify progressive JPEG files. If you run
exiftool *.jpg it will print out the metadata of every
.jpg file in the current directory. You can use a more complicated exiftool command line to print out only the filenames of progressively-encoded files, like this::
$ exiftool -if '$EncodingProcess =~ /Progressive/' -p '$filename' *.jpg
6 files failed condition
5 image files read
If you want to look across multiple directories, it can do that too:
exiftool -if '$EncodingProcess =~ /Progressive/' -p '$directory/$filename' -ext jpg -r .
Just run the above command exactly as-is in the top-level directory below which all of your images are collected. Or, if you want, run it from anywhere, and replace the
. at the end (which means "use this directory") with the full path to your files, like
"/Users/yrg/Desktop/Photo Collection", making sure to include the
" quote marks if you have a space in the name.