Installing in my Amazon instance some image manipulation tools, I want to share the two command-lines that saved me a lot of time in this post: (credits given)

Go to https://wkhtmltopdf.org/downloads.html and depending on your version download the CentOS, for me the right was

CentOS 7

x86_64

sudo yum install yourDownloaded.rpm
sudo yum install ImageMagick

Then you can simple take screenshots of the web using :
wkhtmltoimage

and convert them to any format that you like. The image of this post is a screenshot ot the Zeit newspaper converted to -monochrome also:

convert your-image.png -monochrome output-image.png