How do I upload an image from the clipboard just by pasting an already copied image?

I built a site with RoR to upload memes but the uploading method it's through the default upload button where the user have to search for the image in his local device. This It's very tedious and now I want to make it easier for everyone, just like facebook or twitter.
So does anyone know a way to upload images by pasting what's on the clipboard. Something exactly like this https://pasteboard.co/ ?

I've never done it, but looks like you can do this: https://stackoverflow.com/questions/490908/paste-an-image-from-clipboard-using-javascript/4400761