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 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.