jsf:graphicImage takes a url to the image,
to render image  object you should:
1) make sure the image object (your entity  or at least its image field) is available after request,
for example if your managed bean scope is request the object will be wiped out
2) create a mechanism to convert object refrence to a url and back
3) give the image refrence as url to jsf:graphicImage

if you want a simpler approach use seam image tag!
this way you will just give the image field  name to the seam jsf  image tag, and it works!