I know this post is old, but maybe might help someone else in the future. personally I think i was using maybe Xshare , xbox gamebar or windows gamebar, to basically freeze my screen, and at the same time Gyazo would launch instantly and i could click & drag to start making a box. once i release the click, a screenshot is automatically saved on pc, and uploaded to the website.

Used this method a lot in video games, to showcase or trade items Fast & easy. Especially if i was making an item shop or something. Can turn a 1 hour project shop of 500 items into just a couple minutes.