Hi aine07
Sorry, are you asking whether the prosecution NEED photographic evidence in the situation as you have described i.e. driver not detained in car or whether, IF they have it, should it be disclosed pre-charge?.
As JNO states, yes, a person can be prosecuted for drink driving even after they have got home but if they claim they had comsumed alcohol after driving then post-driving onsumption and back calculations are required by an expert witness.