It’s an invasion of privacy because it’s not neutral info. It may for example contain information about genetic diseases or other things that could be used to discriminate against you. It doesn’t matter if it’s not the police’s intent to use it that way, since by collecting it they create a huge target for hackers to get a large amount of this info. The information it contains should be considered closer to CC number than a ID picture (or arguably even worse, since you can’t change it).