Also, the profile picture and avatar picture are two separate settings. To see the avatar (little picture next to your posts) you need to load an avatar. The profile picture only shows up when someone visits your profile.
Each setup can be found under Edit Profile Picture and Edit Avatar on the User CP page, as Tim suggested.
Addendum: It has been reported that if you are using the Tapatalk app to access the forum you can upload Avatars directly from the iPad. That is the only (easy) method I've heard of that will work from the iPad. This is not the same app as the iPF (Discussion Forum for iPad Users) app.