Underneath a text field using to write a post you may see input field with two buttons.
First one "Przeglądaj", let's say it means "choose folder".
Press it, choose your jpg file not bigger than 300 kB and not wider than 800 px.
Press "dodaj obrazek" which means "upload file".
Wait a while till a picture upload. After that it should be visible.
Finally press a button with green word "odpowiedz" which means "answer" or "dodaj wątek" means "add topic", depend whether you answering or creating new topic.
Thanks for a link to your article also.
BTW you sent some wavy cyanescens pics to our email.