Add height constraint

[gramound]

Hi, thanks for creating this. I use it for debugging Android remotely using screenshots instead of a webcam. I have one feature request: when displaying the image in my terminal, I would like to be able to constrain the height to avoid scrolling past the visible area.

[pnappa]

Great idea - for now, you can get around this by specifying width (and you can derive the expected height as you should know your aspect ratio of your image).