Per GPG guidelines, photo IDs should be about 240x288 pixels and 4k-6k in size. I used: convert -resize 240x240 -quality 75 original.jpg gpguid.jpg. However, the resulting file is still 17k. Specifically, I am curious what options I have before decreasing the quality level.
This is the command I settled on: convert -resize 240x240 -quality 55 -strip -sampling-factor 4:2:0 original.jpg gpguid.jpg.
The original command yielded a file that was 17,169 bytes. The -strip argument brought the size down to 10,226 bytes by removing profiles and comments. The -sampling-factor argument reduced the size to 8,315 bytes by cutting the chroma channel's resolution in half without affecting the luminance resolution. Finally, turning down the quality to 55 brought me within the recommended 6K.