Add "Welcome Box" to homepage (posts page)

Hi! I’m trying to add a picture to the beginning of my homepage, which is also my posts page. I would like the picture to appear below the header but above the posts and only on this page. Does anyone know a good plug in or hack that can do this? I can get it to work on the other pages, but I can’t seem to get it to appear on the homepage.

Thanks so much!