Dr. Daragh Murray:

In the UK, they are. It is a complicated legal situation in that they are not necessarily supposed to be and a person has the right to revoke them but as it stands, they are held indefinitely. Other reference images can be used, for example, if you are carrying out a search using retrospective facial recognition, possibly the image you are looking for is from social media or an image a police officer has taken. The really big reference database is the police national database.