In the UK, the latest driving licenses are in black and white, which is
mentioned as an enhanced security feature, so a different eye colour
would not be a problem on those :-)

http://www.direct.gov.uk/en/Motoring/DriverLicensing/DG_068315

We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember "AnotherD@rnedSock" <
@> saying something like:

Genuine LOL!

Aye, it's getting harder to enter the Western Isles.

Should have done some subtle PlaStic surgery on him, so that
cumulatively he looked just enough like himself to fool him, but
different enough to get a security bod interested.

The main concern seems to be to allow face recognition software to read
the photograph properly, so it needs to check various points on the face
carefully, and when combined, those points would be unique to only a
small proportion of people. If someone's face is on a wanted list, an
alarm could be triggered, and further investigation would follow. I
would expect that in future, when you hand over your passport, the
photograph will be scanned and compared to an actual picture of your
face, taken from a nearby security camera, this way, if the pictures
don't tally exactly, again it will trigger an alarm, this would help to
cut out human error when immigration personnel are busy and could miss
slight differences. Face recognition software could also help if someone
is using multiple passports with the same picture and different names,
as this could also trigger an alarm, so passport photos need to be very
clear on facial features like the position of the eyes, nose and mouth,
and possibly ears, and if these are not clear, the photo will probably
be rejected.

And also that they're printed "professionally", and that photographs
printed at home are not likely to be of an acceptable quality, it would
appear!