General rule of thumb found in the CHYOA formatting rulebook.  The exclamation mark is important because the website is being told that, if the format goes through, you're sending an image and not a link.
Furthermore, if your image comes out empty, then it's the provider's/host's fault. Best to do is to upload it in a cloud or image uploading site such as imgur or pixxxels.cc
I write everything on my phone. I want to download pictures to my phone then insert them. Is that possible?
Unfortunately no, you cannot directly upload photos into stories by phone. Fret not however, as you only need to find a website that allows uploading of photos in phones (maybe Google Images but don't quote me on that), find their link, and paste the URL with brackets. And remember the rule of thumb: !(title)
I have a blogspot page I use just for uploading pictures. It only takes a minute to set up and I always know where my pics are in case I need to relink them.
If you would download an image, that means it's already on the Internet in the first place. Provided it's a stable source (e.g. a year-old Hentai Foundry drawing probably won't be deleted), you can just use the URL from wherever you found the image.
