1. Make sure the picture you want to post is on a publicly accessible site such as imagecoast. You canNOT post a picture directly from your personal computer or phone. Let's suppose you put pics on "hostsite".  Make note of or copy the url: hostsite.com/accounts/elegance39/mypics/picture01.jpg (that's made up; use the real address).

2. The TER posting form has several sections.  Fill them in, such as:

subject: Picture hosting site + fill in the blanks
message: 1. Make sure the picture you want ...

I'm not including a LINK to a website, so I'm leaving the next two sections blank. But I am going to include a link to a publicly accessible public domain picture, a Happy New Year pic with this URL  
https://image.freepik.com/free-vector/vintage-2017-new-year-background_23-2147574532.jpg which goes in the "picture URL" box, making sure that there is one and only one "http://" or "https://"  

That should do it.

link URL:  
link title:  
picture URL: https://image.freepik.com/free-vector/vintage-2017-new-year-background_23-2147574532.jpg