Thomas Scanlon, 23, attacked Jamie Bagnall with a piece of wood at a flat in Pensarn near Rhyl, Denbighshire, Mold Crown Court heard.
Scanlon, of no fixed abode but who had lived at Rhos-on-Sea, admitted wounding with intent to do grievous bodily harm.
On Monday, he was jailed for four-and-a-half years.
Prosecuting barrister James Coutts said Scanlon was in a relationship with Mr Bagnall's sister. It was accepted Mr Bagnall had stolen an iPad from her, and the defendant had made a threat to "get" him.
The court heard that after the attack in March 2015, he posted the photograph of Mr Bagnall cowering on the floor on Facebook with a caption which read "I am sorry, ha, ha, ha".
Mr Bagnall, who has since moved to the Manchester area, needed surgery, had severe injuries including four deep cuts to the head and an injury to his elbow.
Owen Edwards, defending, said he appreciated that he had got himself into a huge amount of trouble.
Judge Niclas Parry told him: "This was a revenge attack - a total over-reaction to a dispute between you and Mr Bagnall."
A 10-year restraining order was made preventing him from contacting Mr Bagnall.

A ceremony at India Gate will be an opportunity to honour a sacrifice that was in the past overlooked in both Britain and India.
The 70,000 Indian soldiers who fought and died for the British during World War One were once viewed in India as part of its difficult colonial history.
In a day devoted to paying tribute, William and Kate will also, quite literally, retrace Mahatma Gandhi's final footsteps before he was murdered.
The country's founding father - who once declared that non-violence, was a weapon for the brave - had a vision, which wasn't realised, of an independent, united land.
It was Prince William's relative, Louis Mountbatten - the last Viceroy - who oversaw the creation of India and Pakistan.
Prince William, with his wife, will end the day by speaking about his grandmother - a woman soon to turn 90, who's Britain's longest reigning monarch but who was never Queen Empress of India.

The 37-year-old woman and 42-year-old man were pronounced dead at the scene.
A further two people are in a critical condition and a third has been described as "serious".
The crash, which involved a silver Mercedes car and a white Vauxhall van, happened on the eastbound carriageway between Polmont and Linlithgow at about 21:00 on Friday.
Anyone who witnessed the crash is asked to contact police.
A Police Scotland spokeswoman said: "This has been a serious road traffic collision.
"We are keen to hear from anyone who witnessed it or who has information that can assist us in our inquiries."
A man who attacked another man in a row over a stolen iPad and then posted a photograph of his injured victim on social media has been jailed.
[NEXT_CONCEPT]
The Duke and Duchess of Cambridge's first official visit to India moves on to New Delhi.
[NEXT_CONCEPT]
A nine-year-old girl has died, along with a man and woman, in a crash on the M9 in West Lothian.