OTTAWA - The federal Liberal party has apologized for posting a doctored photo on its website that depicts Prime Minister Stephen Harper being assassinated.

The photo -- in which Harper's face was Photoshopped onto the famous picture of Jack Ruby gunning down Lee Harvey Oswald -- was removed immediately after it began drawing public notice.

Another fake photo, depicting Harper with his arm buried to the elbow in the wrong end of a cow, was also removed.

Party spokesman Dan Lauzon said the cow picture was meant to poke fun at the carbon emissions produced by bovine flatulence but was removed "due to the possibility of misinterpretation."

The photos had been part of a contest, in which the party invited people to make up humorous pictures portraying the prime minister's reluctance to participate in the Copenhagen climate-change summit.

The photos are "user-generated" and don't necessarily reflect the views of the party, said Lauzon -- still, they are supposed to be screened by the party before they're posted.

"We do review them but that one admittedly slipped through the cracks," Lauzon said of the doctored photo of Oswald, who was shot by Ruby on Nov. 24, 1963, two days after Oswald was arrested for the assassination of U.S. President John F. Kennedy.

"We removed it immediately and we apologize to anyone who was offended."

The party posted an apology on its website as well.

Although Conservatives drew the offending photos to reporters' attention, the Prime Minister's Office declined comment.

"We won't dignify this with a response," said Harper spokesman Dimitri Soudas.

Soudas said Liberal Leader Michael Ignatieff "should comment, not us, as the incident reflects on Mr. Ignatieff's judgment."

Liberals said Ignatieff had nothing to do with the photo contest or the website.

The Tories have been forced to apologize themselves in the past for inappropriate images on their party website.

During last year's election campaign, the Conservatives had to remove an image of a puffin pooping on the shoulder of Stephane Dion, then Liberal leader.