All that is going on is the moderators need to approve it and this takes a long time. Heres what gpes on:
1) You upload your pic.
2) You set it as your profile pic or put it elsewhere.
3) The mods approve the picture.
4) Wait a couple of days.
5) If it doesn't show up after 7 days then look at the log-in box and you will find a message saying 'STOP. Your picture wasn't approved.'
6) If step 5 didn't happen then you'll see your new pic after a day or two!
Hope this help! : D
There's a ninja somewhere in this signiture...