Posting a picture into a discussion thread is not difficult. 
Once you learn how to do it you will be posting pictures in under one minute.  Honest! 

Here's an overview of what you need to do. 
Following are detailed pictures that walk you through the process step-by-step.
 

Overview:

1.  You have taken your picture and stored it in a folder on your computer.

2.  You will next need to copy that picture somewhere other than on your computer.  This is known as Photo Hosting. 
     A great photo hosting service is PhotoBucket - and they're free!  You can find them at http://www.photobucket.com

3.  It only take a few moments to sign up for a free PhotoBucket account.

4.  Once you've opened your account you will have a main "album". You can upload your pictures into that main album.  You can
     also created "sub-albums" (which is a handy way to keep things organized).

5.  Once you have uploaded your pictures you copy everything that is in the TAG field and paste it into the discussion.  This
     copy-and-paste procedure is very similar to the copy-and-paste procedure you perform in your word processor.