Bhai mostly hm log 2 Tarike se Image Post karte hai.
1. Firstly Change In to Desktop View .
If You Want to upload a photo from your pc/mobile and post in to thread so while creating Post You Will See a attachment bar. Click On That Bar and Upload Image , You Want . After uploading you will see your name of photo . See @ front of Photo You will see a button like Post Attachment . Click On That . Your Photo Will Be Added To Your Post .

2. Copy Any Image Url and Add that in to post .
Use Coding [IMG] http://Your Image URL.jpg[/IMG] (Image could be in .png/.jpg/.jpeg And Don't Forget To Remove Space After [IMG] coding.)
[b]Example:-

Above Image's Coding is [IMG] http://tricksduniya.com/images/logo.png[/IMG]