The ability to post links, images, etc. is controlled by your ‘Trust Level’ in the forum software.
The more interaction that you have with the forum, more posts read and made. more “'likes” and other feedback given, and so on, then your ‘Trust Level’ changes and you are able to post more types of things.
This old’ish blog describes basically how it works, but it is a bit old so may not be entirely up to date, and the settings themselves can be customised to suit the needs of a particular forum.
So don’t use the numbers quoted in this blog as a set-in-stone guide to what should happen here at the CCleaner forum, because the Trust Levels, and how to qualify for each level, will almost certainly have been set differently to what it says here.
This article is just how it works in general: