Humberside Police is investigating the theft of several sheep over the past few months from the same location near Howden.
The most recent offence happened between 8.30pm and 10.30pm on Sunday.
Two pedigree Blue Faced Leicester male sheep were stolen from a field near Howden Dyke Road, Howden.
Both animals are tagged with numbers 4361K001 and 436K002, and are also data tagged.
Four other pedigree sheep, three Blue Faced Leicester and a Southdown, have been stolen from the same location in August and November 2018.
Two people are thought to be involved in the offences, one of which is shown in the CCTV image, the force said in its appeal.
Anyone with information is asked to call 101, quoting 16/19638/19.
People can also call Crimestoppers anonymously on 0800 555 111, quoting the same reference number.