As many as 2 million drivers could face £1,000 fines for failing to update the photo on their driving licence, according to the Driver and Vehicle Licensing Agency (DVLA).
The photo on your driving licence needs to be updated every 10 years - and failing to do so would invalidate your licence and could leave you with a £1,000 fine if pulled over by the police.
But as many as 2 million have not updated their photo, leaving them vulnerable to a nasty surprise if stopped with an invalid driving licence.
The DVLA says it sends reminders out two months before a renewal is due.
A spokesperson for the authority says: "Appearances can change and it is important that photo card licences are updated every 10 years to ensure the police and other enforcement agencies have the best possible photograph to help them correctly identify whether a driving licence is being used fraudulently.
"This helps prevent driving licence impersonation - stopping disqualified and perhaps dangerous drivers taking to our roads."
What can you do to make sure you don't fall foul of the photo regulations?
Update your photo online
You can do it online at https://www.gov.uk/change-photo-driving-licence if you have a valid UK passport issued in the last five year.
The renewal is done using a Government Gateway ID, so if you don't have one already you will need to register. It will cost you £20. You'll also need your National Insurance number, your current driving licence and your addresses for the past three years.
Do it in the Post Office
You'll need to get hold of a D798 form that will either be sent to you by the DVLA or can be picked up at selected Post Offices. If you are sent a form it will list the closest Post Offices where you can renew your photo.
These can also be found on the Post Office website or by calling 0845 722 3344. You can renew your photo in the Post Office with a completed D798 form, your driving licence and paper counterpart and a fee of £20. The Post Office will charge a fee of £4.50 to process your application.
Apply by post
Alternatively, you can apply by post, for which you'll again need a D798 form, a passport-style photo taken within the last month, your driving licence and a cheque or postal order for £20. Send your application to DVLA, Swansea, SA99 1DH.
When else to change your licence
Your licence also needs to be updated if you change your address or change your name. On both occasions, there is no fee.