I've got storing and posting photos down to a routine now, to the point where I've stopped thinking about how it's working.
Pictures go on my account on Imgur, and I use a desktop app called ShareX to put them there as a drag-and-drop operation. Then a reference to a picture with an initial thumbnail is:
[url=full_image_address][img]thumbnail_address[/img][/url]
Imgur makes this very easy, because they let you show one of your pictures in thumbnail form just by using the same name with a 't' added before the ".jpg" part of the URL.