Right now, jpegoptim < v. 1.3, its newest version which is very fresh and still will take some time until 1.3 hits all major Linux repositories, cannot save JPG as progressive.
JPEGtran can save progressive JPGs. As we are already using JPEGrescan after jpegoptim: Make a round of tests of JPEGrescan vs. JPGtran and if JPEGtran is a valid alternative, then use it and make sure output JPGs are set to be progressive per default.
Right now, jpegoptim < v. 1.3, its newest version which is very fresh and still will take some time until 1.3 hits all major Linux repositories, cannot save JPG as progressive.
JPEGtran can save progressive JPGs. As we are already using JPEGrescan after jpegoptim: Make a round of tests of JPEGrescan vs. JPGtran and if JPEGtran is a valid alternative, then use it and make sure output JPGs are set to be progressive per default.
Command: jpegtran -optimize -progressive -outfile outputfilename.jpg