The reason, if I am not mistaken is so that they can attach a picture of the patient with the patient records to provide a better quality of care. You become a person with a name, rather than just a name and a number.
Imagine if you had short meetings with dozens of people a day and you took copious noted of those meetings. Then weeks later, one of those people calls you and asks you about the meeting. Just referring to the notes, you may not remember the person, or for that matter, anything else from the meeting that wasn't in the notes. With a picture, they can remember much, much more. There is no invasion of privacy. And is covered under HIPPA.
As for asking for ID, I've been going to the same small office for 7 years and I still have to show my ID and insurance card every time I come in. It is their duty to insure no one is masquerading as you in order to illegally obtain prescriptions or to double dip on insurance.