You just need to be active. If I remember correctly you need atleast Jr member to post images. This is mainly to prevent spam. You can see the ranks and the required activity here: https://bitcointalk.org/index.php?topic=178608.0

To maximize your activity, you need to post atleast twice once a day(though it doesn't mean you should post random sht. Post something constructive). So you need probably around 15 30 days to get Jr member from 0 activity.

EDIT: Thanks for correcting me random poster friends.