Photographs of reusable mineral-water bottle caps, each labelled with the date stamp printed on the cap. The dataset was collected to study the reuse lifecycle of returnable glass bottles: The date plus two years (shelf life date) is printed on every cap at filling time, so reading it off returned empties allows the round-trip (fill → return) duration to be measured. The setup for taking the photographs involved diffusive light to minimize… See the full description on the dataset page: https://huggingface.co/datasets/aihpi/bottle-cap-date-stamps.