Ward adjudged Danny Shittu to have tripped Grant Hanley in the area with 12 minutes to go and Jordan Rhodes scored from the spot to move Rovers above their hosts and five points clear of the drop.
"That decision has cost us," said Jackett. "I've just seen it again and it looked like a soft decision, in my opinion the referee got it wrong, it didn't look like there was any contact.
"I was looking for the refereeing team to make the right call as it looked soft at the time, and having seen it again it was."
Shittu's protests at the final whistle earned him a red card and Jackett added: "Danny's very upset, but I have to back my player.
"He's a passionate man and he felt very passionately that there was no contact. Unfortunately it was a second yellow which we cannot appeal."