Comment I could live with rapid deletion (Score 1) 49
I would prefer not having these cameras at all. If you need to read license plates, hire people to do the jobs. If it's that important, it's worth paying for.
But that's not going to happen.
So, I can live with destroying all images within seconds unless there was an actual need to keep them, then keeping them and the data gathered from them in an encrypted, non-network-accessible location only for as long as they are needed, with strong oversight to make sure images really are deleted when no longer needed. Any supposed "need" to keep these images beyond, say, the time it takes to send out a you-didn't-pay-your-toll-bill invoice and give the recipient an opportunity to pay or protest should require court oversight.
In rare cases where the police are "on the lookout" for car matching a general description ("driver in green station wagon kidnapped small child from Springfield Kwik-E-Mart, no license plate"), keeping all images within a small targeted search area for hours instead of seconds may be tolerable, with the police keeping only those images that are useful for the investigation after the several hours have expired. In any case, keep the images offline.
In any case, keep the images encrypted and offline. I don't want some overseas black-hat group collecting a dossier of my car's travels.