I use Imgur
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. You can paste the code in and use the Preview button to see how it looks without actually posting. The width= and height= parts are optional. If you picture is way too big, you can set those sizes so it takes up less space in the post. Once posted, clicking the picture will show it full size.
[img width=252 height=374]https://i.imgur.com/xN2IPO0.png[/img]update
: found a much easier cut-and-paste feature on Imgur. Adding a screenshot below as this question gets asked quite frequently so going to link people here.
(Hover over your uploaded picture to get the gray Copy Link
button to show up)