Feature Request: Read image from clipboard

[ajmeese7]

I'd like to have a flag like --clipboard or --paste that will read an image from the user's clipboard and run the script on that. This is useful for if you're grabbing a still from an image file and you don't want to go through the hassle of saving it to the disk if you don't even know if it's going to work.

Some quick research shows that something like xclip -selection clipboard -o should do the trick, I want to look into making a PR myself when I have the time but I wanted to go ahead and make an issue in case somebody gets to it before me.