Former Shamrock player Sheppard, 21, will stay at the Crown Ground until January.
"I have six months to impress really," he told Accrington's official club website. "Paul Cook is all about his strikers scoring so hopefully I can be one of those.
"He likes to play a nice brand of football and likes his strikers to score goals, so that's what drew me towards this."
Accrington boss Cook, who saw Sheppard up close when he managed Sligo Rovers in Ireland, is confident Sheppard will bring goals to his side.
"We're absolutely delighted to have got Karl in and we can't thank Reading enough for letting us have him," he said. "He's a lad who needs to be playing games and I think you could see from his finish on Saturday [during Accrington's 4-1 defeat to Coventry] that if we get him in the right areas he'll score goals."