The rule totally makes sense, but I was wonderign if images posted in "older" posts will be automatically shown if status changed.
Yes, once your rank is higher than newbie, the images in your post will automatically displayed.
When can we as junior post pictures?
When your rank is higher than Newbie (i.e when your activity is above 30). You'll then become a Junior Member and every image that you embed in a post could be displayed.