Use imgur.com They are free, you don't need to open an account and it's just a matter of getting the image URL then inserting that URL into a post in here.
Don't use your local DropBox/OneDrive URL as only you would see the image. A public URL is needed.
Just paste the sequence of characters taken from imgur (or your other image hosting site) that looks like this:
[img]https://i.imgur.com/X9pAwC6.png[/img]
Hey presto. Your image appears!