To post a picture, follow these steps.
Step 1: Upload your picture to any picture hosting site. Eg:
Photobucket or
Tinypic. I recommend Tinypic because you do not need to register to upload.
Step 2: Copy the img code for forum of the picture.
Step 3: Click the 16th button on the top when you are posting a new topic. Example at the picture below.
Step 4: Paste the img code on the text box and press ok. Look at picture below.
Step 5: There will be a code shown in the text but when you have finished the topic and clicked send, you will see the picture.