Rounded corners

I have a banner and need a circular edge on the bottom right hand corner only. I have looked at a few tutorials, however I cant figure out how to apply a rounded edge to one corner only.

basically this http://shapeshed.com/journal/curving_the_edges_of_images_in_photoshop/ but with only one corner rounded.

Bear in mind the banner is a photo as opposed to a block of color.

Any ideas would be most welcome

try this, it's real quick but depending on what your doing could be many ways
make a selection near the corner inverse it then use the eraser tool