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(CNN) -- When the seventh annual San Diego Comic-Con took place in 1976, the gathering of a few thousand fans was just what its name implied: a convention about comic books.
That year, however, Lucasfilm Ltd. set up a booth and held a slideshow presentation about a movie nearly a year away from release, "Star Wars."
More than 30 years later, the convention appears to be more and more a place where movie studios and television networks can follow in the footsteps of "Star Wars'" by giving hard-core fans an early look at upcoming releases.
Sometimes, it's a very early look. Walt Disney Pictures came to Comic-Con in 2008 with test footage from what was then referred to as "TR2N," a sequel to the 1982 cult classic "Tron," one of the first films to use computer-generated imagery. The special effects and appearance by Jeff Bridges, reprising his role in the original, made a big splash with the audience, even though the footage likely won't be in the final version of the movie, now called "Tron: Legacy."
"When we brought our 'Tron' test footage to Comic-Con, we knew that the crowd in Hall H would tell us, almost instantaneously, if there was an appetite for this film," said Sean Bailey, president of Walt Disney Studios Motion Picture Production. "The influentials in San Diego can generate global buzz, and we've been fortunate that they have embraced our project."
That reaction from Comic-Con more than 2½ years before its December 17 release has kept fans closely following the movie's progress. On Thursday, cast and crew from the film will return to the convention for the third year in a row and likely will present new footage to continue to build fan intensity around the movie.
It also will be "The Green Hornet's" second year of having a presence at Comic-Con. The movie won't be released until January, but last year star Seth Rogen was there to talk it up and show off the Green Hornet's car, the Black Beauty.
Jon Favreau is someone who can attest to the power of Comic-Con. The actor-director has been quoted as saying he was fairly nervous about how "Iron Man" would be received when its teaser trailer debuted at Comic-Con three years ago.
"In the Marvel universe, [Iron Man] is a top-tier character, but most didn't know who the heck he was," said Vic Holtreman of Screenrant.com, a panelist at this year's convention. "Favreau did such a good job of hitting it right."
After last year's return to Comic-Con to promote "Iron Man 2," Favreau will be back once again with "Cowboys & Aliens," his next movie that's still in production and won't be released for another year.
The studios behind "Iron Man," Paramount and Marvel, also will present a panel for "Captain America: The First Avenger," even though it is still a year away from release.
Movie studios aren't alone in this practice: Steven Spielberg's upcoming television series, "Terra Nova," had a panel scheduled for several days before it was canceled, reportedly due to a lack of footage available to show fans.
All of this might lead one to ask, why the rush?
"Marketing continues to expand, and the studios and distributors are looking for every opportunity to show upcoming movies to the most enthusiastic press and fan base, and Comic-Con is exactly that," said David Gross of Moviereviewintelligence.com. "Movie information, like all information, is accelerating in speed."
Social media, which is prevalent at Comic-Con, is a big part of that. "Movie reviews are flying around faster than ever," Gross said. "People are sending messages to their friends as they are seeing movies, and it's moving a lot faster."
This swift reaction can also apply to the early footage shown at Comic-Con, where attendees can send out instant feedback to anything they see there.
In the case of "Iron Man," which had its debut even before the popularity of sites such as Twitter, that can be a good thing.
At the same time, early positive buzz doesn't always translate to box-office success.
" 'Kick-Ass' was the most buzzed-about thing from Comic-Con last year," panelist Holtreman said. "After walking out of there, you would think it was gonna make $200 million." ("Kick-Ass" reportedly has yet to gross $50 million.)
Despite such cautionary tales, dozens of new movie and TV properties will be at Comic-Con this week, hoping to make a good impression on throngs of potential viewers not afraid to give feedback.
Gross calls this part of the democratization of information: "It's good for the consumer in the end," he said.