victor prout created a makeshift dark room on board a boat he used to travel along stretch of the river thames .
prout captured images of iconic landmarks in the 1850s , such as the houses of parliament and windsor castle .
images are oldest surviving documented record along the river and are remarkably similar to those of today .
collection , contained in the book of the thames , is to be sold for almost £ 30,000 at the oxford book fair .