The LGBT News site Good As You points out that the group New Hampshire for Marriage, a project of NOM, used a screenshot of a 2008 campaign rally for President Obama in Columbus, Ohio, on their site. The picture, from Reuters, shows around 60,000 people who turned out for Obama back then, according to the blog Upper Arlington Progressive Action.
The Obama rally picture is photoshopped next to a person holding a "Defend Marriage" sign. "NH for Marriage is a coalition of Granite State citizens committed to defending traditional marriage in New Hampshire," the caption says. "Our goal is to repeal the state's same-sex marriage law by turning the tide against out-of-state special interest money that fueled its passage and corrupted our political and legislative process."
Here's a screenshot from their site:
Good As You grabbed another example of NHFM using the picture here.