As far as I'm aware, adding images is allowed for users in the MOSC forum, but results in an "unauthorized" error in the OTN forum. The insert image and video button used to be disabled.
I have not really looked into it, but perhaps people created a post on MOSC, which allows to attach images, and then moved the post to an OTN forum. However, you can create a document, where you can insert images and that is allowed OTN too.
The UI is confusing but the [OTN] Forums FAQ (https://wikis.oracle.com/display/Forums/Forums+FAQ) contains this statement very near the bottom:
Can I attach files to my messages?
Sorry, due to security and legal reasons, attachments are not supported.
I assume that applies to images.
As Catch-22 noted, attaching files is supported in the MOSC. The author of a thread can move their messages between the OTN and MOSC - at least that is how I did it.
have a good day,
Some of the information is also incorrect: "All your friends' posts will be displayed in your communications stream."
When you "friend" someone, you are automatically Following each other and information updates go to to the Dashboard. I have actually tested this a couple of times. I explained it in Oracle Community Forum Guide - Part 3/3, chapter 6.1. The situation explained in the FAQ applies to Tracking a user, which I outlined in chapter 184.108.40.206.