In order to post photos in the forum, you’ll need to use a separate image hosting service. One simple option (but certainly not the only one) is https://imgbb.com/
Create an account, and upload any photos you’d like to post in your thread. Once you’ve uploaded your photo, the site will give you a list of possible embed codes. Select “HTML Image” and copy and paste the link below into your post. Once you hit “Submit” on the forum page, your photo should appear!