In PDF/X-1a, a tagged gray JPEG that the Compression settings keep as
JPEG was decoded and written with Flate. It is now written with its
JPEG data unchanged, in DeviceGray without its profile.
A PNG or JPEG embedded as it is now has its gray or RGB profile checked
with valid_icc, like the images the recoder writes: a malformed profile
is left out, the JPEG keeping its JPEG data and the PNG decoded.