According to HuffPo, this image is being ciruculated in Tea Party circles as a true representation of the protest on Sept, 12:

original.jpg
The image is real but it does not represent the Tea Party event but one that happened before 2004:
There's another big problem with the photograph: it doesn't include the National Museum of the American Indian, a building located at the corner of Fourth St. and Independence Ave. that opened on Sept. 14, 2004. (Looking at the photograph, the building should be in the upper right hand corner of the National Mall, next to the Air and Space Museum.) That means the picture was taken before the museum opened exactly five years ago. So clearly the photo doesn't show the "tea party" crowd from the Sept. 12 protest.
So the status of the image is the same as that of Obama's Kenyan birth certificate. For Tea people, the present truth is so painful that any old lie offers some comfort.