How Google takes feedback 14 years ago
Open source solution : http://experiments.hertzen.com/jsfeedback/
It uses html2canvas to generate site screenshot on client side.
[ my public key: https://keybase.io/premist; my proof: https://keybase.io/premist/sigs/foKFpKanf-FQVZ96caK272do34WUW929tVjd4YTsPG4 ]