On a computer, nothing is easier than snag.gy. Just open your photo in Paint, press ctrl-A, ctrl-C, then open snag.gy. You may also upload a screen capture by press the PrintScreen key or Alt-PrintScreen.
On a phone, I found the easiest is to use imgbb.com. Once you uploaded the photo or screen capture to imgbb, touch on the image icon, the uploaded photo will be opened. Touch and hold on the opened image and you get the URL.