Your profile picture is what's shown on your profile page only (click here
). What you're probably thinking of is your avatar, which is an image that shows up on the left in the forums under your username (like mine is of me scuba diving). They're 2 different things in the forum software, so if you want to use the same photo for both you just have to set it in 2 places.
To set your avatar, goto your User CP, and on the left is a link that says "Edit Avatar". Click that, then select your photo.
Moving this to the Forum Admin / Tech Support forum as well.