A profile picture is the one that people see when they look at your profile (and I can see your picture there). The one that shows on the posts is called an Avatar and you can also upload the picture for that in your User Control Panal under the Edit Avatar option.
Ah, yes indeed. I just assumed that the photo displayed with our post is called a "profile photo", as in Facebook. An avatar seemed to be something used in video games. Ok, much thanks. I'll fix it.