How I usually post non-sylestia pics is that I'll first upload them to an image sharing website (I use imgbb. You can also use things like instagram, etc, as long as you can get an image link)
Once you have that link copied, hit the blue IMG button on your forum post and paste your link in the tags that appear.

A working image should look like this (make sure the image you're posting has the file extension at the end in something like a .png, .gif, or .jpg format otherwise this won't work)