Stringent new international photograph standards will have to be met by all UK passport applicants as of next week, officials warn.
New biometric passports are in the pipeline
The international rules, designed to combat fraud, will make new UK passports compatible with facial recognition technology.
From 12 September, pictures will have to be taken against an off-white, cream or light grey ground.
Subjects must look straight ahead with mouths shut and "neutral" expressions.
Other rules include the size of the photo - 45mm by 35mm - which must be printed on normal photographic paper.
Applicants must be on their own in the picture and their head and shoulders must take up 65% to 75% of the frame.
Applicants whose pictures do not comply will not have a passport issued until they have supplied a suitable alternative.
The pictures will be used for new biometric passports, which will be issued from the beginning of next year.
These will contain chips which can be scanned to reveal the holder's facial image.
Bernard Herdan, chief executive of the UK Passports Agency, said it was "very important" applicants checked their photographs complied with the rules.
Holders of existing passports do not need to have them updated but will have to comply with the new rules when they apply for replacements.
Home Office Minister Andy Burnham said: "The British passport is currently one of the most secure in the world, but would not stay that way were we to stand still.
"The UK Passport Service and its equivalents in countries all over the world are constantly working to enhance passport security to stay ahead of forgers and fraudsters."
The photo rules are set out in a leaflet contained in the standard passport application pack and also available from the agency's website.