From Sociological Images:
The Florida Family Policy Council [a conservative Christian organization] sent out a message about a judge's ruling to allow a lesbian couple to adopt a relative's child they had been fostering. The FFPC, which opposes gay adoption, sent out an alert to its members and including an image of the couple… well, in theory. On the left is the photo included with the alert; on the right is a photo of the actual couple.
It's very obvious use of a stereotype what lesbians look like as a scare tactic. The actual couple doesn't fit the ideal of the androgynous-looking, angry, mannish lesbian couple. They look like nice middle or upper-middle class professional women who can raise a child perfectly well. They're attractive by mainstream heterosexual norms of femininity. They look happy and non-threatening.They are simply not sufficiently menacing.
As Nicole points out, the couple on the left isn't just a stereotype of lesbians, it's associated with a particular working-class aesthetic, especially the mullets. They aren't thin and conventionally attractive like the couple on the right.
The FFPC says the use of the wrong image was a mistake. Though it seems they've made similar errors before when alerting members about gays and lesbians trying to adopt children.