Nearing its premiere, Warner Brothers, the official distributor of The Dark Knight Rises movie, released a viral marketing campaign as done in the previous movie. Found in the movie’s website is a Gotham City police investigation showing different places Batman was seen. Fans can unlock still frames of the trailer when they tweet the graffitis found in the said places using the hash tag #TDKR07202012.
Image from DarkKnightRises.com

Image from @CypherScar
When the frames were completed, fans tried to collate the significant stills to produce the trailer. Minutes afterwards, Warner Brothers finally released the third trailer online.
Here’s the video. I recommend you watch it at 1080p.
