Resize overlay_image

[drorcohengithub]

I cannot figure out how to resize my homepage image properly.

When I use

header:
overlay_image: /assets/images/sketch.JPG

The wrong part of the image is shown - looks like rectangular cropping applied right at the center of the image.

when I use
header:
image: /assets/images/sketch.JPG

The image is too big and takes up too much of the screen.

Is there any way to scale the images? If not, what is the correct way to crop/resize the image?

Thanks for the great work

[mmistakes]

See #542
Closing as this is a duplicate issue.