Indeed, by the "birthday paradox." And, by the "coupon collector's problem," the expected time to have seen all 30,000 images is about n*log(n) ~= 310,000 rand

Indeed, by the "birthday paradox." And, by the "coupon collector's problem," the expected time to have seen all 30,000 images is about n*log(n) ~= 310,000 random images. https://en.wikipedia.org/wiki/Coupon_collector's_problem https://en.wikipedia.org/wiki/Coupon_collector's_problem