A man in his 40s was assaulted outside a pub in Berkhamsted on Thursday 16 January.
The victim was leaving The Highwayman pub when he was assaulted and suffered bruising as a result.
Officers investigating have released an image of a man they would like to trace and speak to as part of their enquiries.
PC Sue Desmond, who is investigating, said: “We appreciate the image is of low resolution however it is the best version that is available to us, and someone may recognise the man’s stance or clothing.
“We would really like to speak to the man pictured because we believe he may have information that could greatly assist our enquiries.
“We would also like to trace a member of the public who stopped his vehicle outside the pub to go to the victim’s aid after the assault.”
If you recognise the person pictured or were the person who stopped to help the victim after the assault, then please get in touch quoting crime reference 41/6364/20.