The image of airplanes hitting the towers itself may not have incited enough outrage and international support to go to war. The reality is that people would have seen it on the news channels and said "my, how awful" and forgotten about it the next day. The image of those two towers cascading down was played over and over again by the media. This image was adequate to incite enough hatred to motivate congress, and some international support to launch wars of agression against two sovereign nations that had not attacked any other country or threatened to do so.
"Let's go to war with Iraq."
-"But, Iraq hasn't really done anything. The people won't go for it."
"Easily fixed. We'll stage a false attack against our own country."
-"So, we'll claim Iraq attacked us?"
"Oh, no. We'll claim it was mostly Saudis and nobody from Iraq."
-"So, we're going to war with Saudi Arabia, too?"
"No, they're our best friends."
-"Then, how do we use Saudis without blaming Saubi Arabia."
"We say that they're a fringe group of fundamentalists."
-"And those are the kind of fundamentalists they have in Iraq?"
"Not at all! In fact, when those fundamentalists sought help from Iraq, Saddam Hussein turned them down flat. He may be the only person who hates fundamintalist Muslims more than we do."
-"Then how is this going to convince anyone to go to war with Iraq."
"Because we'll tell them to."
-"And why would they believe us?"
"Because it's on TV."
-"Not yet."