At the bottom of this text box, you will see a "file" icon button next to the emoji button. You will be able to upload a file (not sure if this one supports multiple files) including image files. However, with image files, they should be connected to an image-hosting service called Imgur.
If you're able to upload any image files directly to Imgur, that's great, it works! Otherwise, please reply with all the bugs that you may encounter and hopefully we'll be able to fix it, somehow.
If the beta testing isn't working well for our forum, I'll disable it until there's some kind of an update is released.
Questions? Just reply. Thank you!