There are a few places that will host your photos for free and then you can link to those pictures in your Ratsun thread.
Photobucket is laden with advertisements and limits bandwidth as of 2017. Avoid using Photobucket unless you have a paid account.
IMGUR offers direct linking to your photos. That is one option.
Another free website is PostImage.IO - the method for uploading and copying the direct link code is basically the same between websites
Watch this video
1. The first step is obviously to create an account on your desired image host.
2. Now that you've started an account, you can upload photos to your album.
3. Select the image that you want to display on Ratsun and copy the entire direct link or hotlink for forums into memory (right-click, copy / or / ctrl-c)
4. Go to the thread on Ratsun and past the code (from your computer's memory) into the message area. (right-click, paste / or / ctrl-V)