At least in my country the rules regarding number plate placement have statements like "clearly visible", "unobstructed" and "must not be covered by protective

At least in my country the rules regarding number plate placement have statements like "clearly visible", "unobstructed" and "must not be covered by protective materials". I the rules would be similar +/- everywhere. I think this is mostly related to speed cameras and similar tools being able to clearly read the plate number.