You've uploaded your picture as a "profile picture", while instead you should have uploaded it as an "avatar".
Basically, when you go into your settings tab, there are several sub-categories, one of which says "Edit Profile Picture". One below that is "Edit Avatar". That is where you have to upload your avatar to make it visible on the forums
This is actually the wrong place, there's a special Support and Feedback section at MH, where you can ask this kind of stuff.