In this field, the date using an ISO string: YYYY-MM-DD. You must always fill in each of the digits, so if the date is December 1, 1853, your ISO date string would be 1853-01-12. If the year is the only date information we have, then you would enter those numbers only. Input the date of the image’s source rather than the date the image was created.
Even if the year is in brackets in the title, do not put it in brackets in the date field.