There was a lot of speculation about where the cameo appearance of Captain America would appear in The Incredible Hulk, with the prevalent theory being that it would occur in the Arctic in a deleted scene. Well, according to Comic Book Movie, one sharp-eyed fan found the cameo.

The scooper, Pablo, wrote:

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Sorry for my english but I'm from spain, well the captain america is in scene of the Pentagon just before Ross and Blonsky start to talk about the super soldier serum in the WWII there is a portrait and down say Steve Rogers.

So, the seed has been planted from the use of the Super Soldier serum in The Incredible Hulk and this cameo (portrait appearance) to help set-up both The Avengers and The First Avenger: Captain America.