I use imgur.com because it's simple and free (no water marks either). Works from a web browser, or phone, and is automated into my desktop screenshot software. It's only worked one time however. I think I've finally figured out why. After uploading my picture to imgur, posting the actual link from the address bar of the web browser doesn't work. I need to change "imgur.com" in the link to "i.imgur.com". Just a guess, but might be imgur.com is only allowing "i.imgur.com" from forums because they do some kind of extra load balancing.
Just wanted to drop a note here for anyone else wondering how to post a picture if they don't use tapatalk. An example of the bbcode is below.
[img width=252 height=374]https://i.imgur.com/xN2IPO0.png[/img]