as a jr. member you cant post pictures to your posts yet. You need to be a member or higher to be able to post pictures to your posts or even to your signature under your username. They changed this a while ago because jr. members used to be able to post pictures.
Who says it? Jr.member can not post pictures ... Are you kidding me? if you read a lot (especially discussions like this) you should know that Jr.members can post images, provided they post them in the correct format ...
You should try it does it work?