This is an incredibly dramatic photo; and quite graphic. However, I think it tells an important story and is important to include in the article. The United States was sending a very specific message about their work in Iraq, and the picture captures this message effectively. It was on the first page of the story, and there was no prior warning to readers.
I don’t know if it is graphic “enough” to warrant an advisory to the public; perhaps it could be on the second page of the article after one click. Violent pictures are not always bad; this one illustrates a few important points. It shows the news that al-Zarqawi is dead and also conveys how the U.S. is publicizing this information. Although seeing a dead body is certainly shocking, some of the shock value has been reduced because it is a photo of a photo. It could be a "questionable" photo, but I think it's acceptable.