1. Upload the photo that you want to use to Webshots and from there go to your Webshots page for the photo that you want to share.
2. On the right side of the screen you will see a box that says link to this picture and gives a number of sizes that you can use. Select the size you want to use. 500px or 600px is preferable since it's large enough for people to see as a starting point and it still fits the forum rules. Copy the text from either box that's outlined in green here.
3. Come back to the forum and start a new thread or go to the thread that you want to post in. Paste the text from your Webshots page into your post and then submit your post or preview it and then submit it (combined into 1 step here since I can only do 4 pictures per post, and using the Flickr example because the idea is the same, but the code reads slightly differently).