>>106373606
You can do this with magick
for img in *.jpg *.png; do
magick "$img" -strip -quality 85 "${img%.*}.jpg"
done
I'm not sure it's guaranteed to wipe all embedded data. In theory the lower you set quality the more likely data will be wiped.
>>106373601
I don't think there is any guarantee with any images. 4chan images are riskier because there is a userscript for embedding images and viewing them easily.