DPA relates to PERSONAL data and how it is kept.
A pic of your car doesn't constitute personal data.
HOWEVER, if someone gets this pic. and doesn't examine it correctly, but just assumes that because it took a picture, you must've been speeding, and then incorrectly issues you with an offer of a fixed penalty notice or 'go to court', opt to go to court, ask for a copy of the pic (Refer to it as 'advance disclosure' of evidence, they should send you it.) and then let a local rag know about it.
If it goes to court, get a journalist to be there to see it thrown out. Could be entertaining!!