How to post images in the forum?

Sorry, but I'm not able to post any images like screenshots or such.

When I write a post or reply I can copy&paste an image directly into the draft, but on submit the image is gone.

When I press the add image button, a new tab opens.
I'm not able to specify a local path to an image file to be uploaded, only web addresses seem to work.
Unfortunately dropbox links don't seem to work either, as only an error message about the preview shows up.

What is the supposed way to do this?
I don't have an own web server to upload this stuff and I won't set one up just for this damn forum software.

Use the image url (like the url you got from a tool like and insert the URL in the BB codes [ IMG ] url  [ / IMG]