I've seen some posts with a picture attached directly and not by link. These posts have a paperclip icon next to the subject, i tried to find out how to attach a picture without a link, but it seems that i can't figure it out. Could somebody help me how to do it because it will be really easy for me to discuss a topic with an image directly on the post. Thanks alot!

What you are looking for is the ability to attach a file to the post. Unfortunately, normal players don't have this ability as you can see through clicking full editor & preview below the last reply in the thread. By uploading an attachment to a thread will add the paperclip symbol on the post.

Moved to the proper section, check out this guide to link pictures : https://pokemonrevolution.net/forum/viewtopic.php?f=89&t=13194