1-Hit 'Reply' button on post, located just up to the right
2-Scroll down below the Graemlins and check the box with "I want to preview my post and/or attach a file"
3-Click 'Continue'
4-Below your typed reply you'll see a field with 'You may attach a file if you like' above it. You can either insert the URL of the place where the pic is stored [on a Flickr or similar account] or click the 'Browse' button and go to your computer's picture file. Choose the picture you want to attach and click it's name in your computer's file. This will attach or download it to the Treebuzz server.
Again, if you adjust the size to about 550 pixels on the wide dimension we all get to see a full screen pic which is generally big enough.
When you've attached the picture file click 'Continue' and then back out. Be sure to take the time to preview your post to make sure that the picture uploaded. If not, you can go back in and edit your attachment.