<human>: This was a while ago but I just want to know how I should have reacted.

My GF and I are in a long distance relationship, and I went to visit her for a weekend.  She lives in a rougher city with a young population.  One night we went out to eat dinner fairly late at a nicer restaurant.  We were both dressed up and she went in a short dress and heels.  After eating, everything was great and we were going to walk to a convenience store to pick up some stuff for the night.  The way to the convenience store was along a darker street with a bus stop on it, and multiple buses parked along the street.  We walked past the first two buses, and when we came to the third bus, a big bald man with a camera stepped down from the bus.  He quickly aimed his camera down and took a picture of my GF's legs... like waist down ish (we were very close to him).  Now both my GF and I were fairly startled.  I wasn't sure how to even handle this so I just sorta glared at the guy and had my GF walk behind me so that the guy couldn't take another picture.  After we got past that street, my GF was visably upset and asked why I didn't do anything.  I understood why she was upset, but I still was not sure what I should have done.  Should I have confronted the guy?  Do I report him to the police?  Is what he is doing even illegal?

Could you distill the essence of the text into 1-3 sentences?
<bot>: Pervert takes surprise picture of my GF's legs and makes her upset. I just glare at him.  What should I have done instead?