I've done these shops before and usually what I do has already been mentioned about taking the menu to the car for grandma or I will sit at the bar and have a glass of water and discreetly snap the photos. One time I was asked about it from the bartender and I simply stated that I am inquiring into booking a company party and my boss wanted to see the actual restaurant menu for all age groups (kids, seniors, etc). I haven't had any issues, although it did take some time getting used to that scenario. Good luck!